The strongest Atlantic storm of 2020, Hurricane Iota, as seen at 10 a.m. EST November 16. At the time, Iota, a category 5 storm with 160 mph winds and a central pressure of 917 mb, was approaching landfall in northern Nicaragua. (Image credit: NASA Earth Observatory)

The brutal 2020 Atlantic hurricane season has officially ended, after generating an extraordinary 30 named storms (highest on record), 13 hurricanes (second highest on record), and six major hurricanes (tied for second highest on record). But fittingly, the busiest season on record refuses to go out quietly: As of December 1, a low-pressure system with the potential to become Subtropical Storm Kappa was located over the northeastern Atlantic, off the coast of Portugal, with two-day odds of development of 10%.

The 2020 season was notable not only for its record number of named storms (after breaking into the Greek alphabet by the ridiculously early date of September 18), but also for its record number of rapidly intensifying storms (10); and record number of landfalling U.S. named storms (12). Let’s not forget the record-breaking November activity – two catastrophic hurricanes hit Central America in November, including Hurricane Iota, the latest category 5 storm ever recorded in the Atlantic. At least seven hurricanes from 2020 will be worthy of having their names retired: Iota, Eta, Zeta, Delta, Sally, Laura, and Isaias – although there is still no official mechanism for retiring storm names from the Greek alphabet. The record for most names retired in one season was set in 2005, when five hurricanes had their names retired.

(Check out this 76-second animation by Jake Carstens showing the National Hurricane Center (NHC) tropical weather outlooks for the entire season; 42 seconds into the video gets particularly insane, when September starts.)

Figure 1. Every single mile of the U.S. Atlantic coast was under a watch or warning related to tropical cyclones at some point in 2020. (Image credit: National Weather Service, Corpus Christi)

An unprecedented battering of the U.S.

The U.S. suffered an extraordinary 12 landfalls by named storms in 2020, smashing the previous record of nine in 1916. Six hurricanes made a U.S. landfall, tying 2020 with 1985 and 1886 for most U.S. hurricane landfalls. Every single mile of the mainland U.S. Atlantic coast, from Texas to Maine, was under a watch or warning related to tropical cyclones at some point in 2020. Only five counties along that stretch avoided tropical storm-force winds, according to an analysis by Kyle Noel. Louisiana was hit by five named storms, the most ever to make landfall in one season in the state (old record: four in 2002).

Hurricane Laura was the strongest and most damaging landfalling U.S. hurricane of 2020, hitting southwestern Louisiana as a category 4 storm with 150 mph winds on August 27. Laura was tied as the fifth-strongest hurricane on record to make a continental U.S. landfall, and tied the Last Island Hurricane of 1856 as the strongest landfalling hurricane in Louisiana history. Incredibly, on October 9, Hurricane Delta made landfall as a category 2 hurricane with 100 mph winds just 12 miles to the east of where Laura hit. Insurance broker Aon estimates that Laura caused $16 billion in damage, and Delta $4 billion.

Figure 2. The 12 U.S. landfalling named storms in 2020. (Image credit: Steve Bowen, Aon)

Aon estimates that the total U.S. damage from 2020’s hurricanes and tropical storms was $37 billion, ranking as the eighth highest total on record. Fortunately, three of the six hurricanes that hit the U.S. struck relatively sparsely populated portions of the Louisiana coast, so the 2020 damages could have been far worse. Each of the six hurricanes that hit the U.S., however, caused over $1 billion in losses, breaking the record of four billion-dollar hurricanes in a season (adjusted for inflation), set in 2004 and 2005.

Figure 3. Satellite-estimated rainfall from November 1-22, 2020, over Central America, during the time that Hurricane Eta and Hurricane Iota made landfall. (Image credit: NASA Giovanni)

Catastrophic impacts in Central America from Eta and Iota

The most catastrophic Atlantic storm of 2020 was Hurricane Eta, which made landfall in northern Nicaragua on November 3 as a category 4 storm with 140 mph winds. Moving very slowly at landfall, Eta lingered for three days over Central America and the adjacent waters, dropping catastrophic amounts of rainfall in excess of 20 inches in some regions.

Flooding from Eta’s rains killed at least 215 people and left 49 missing, primarily in Guatemala, Honduras, Mexico, and Panama, according to a preliminary tabulation released on November 12 by insurance broker Aon, making Eta the fourth-deadliest Atlantic hurricane to occur in November or December, according to statistics from NHC.

November-landfalling Eta and Iota tormented Honduras and Nicaragua, killing many and wreaking unimaginably costly damages on already fragile economies.

Just two weeks after Hurricane Eta’s devastating impact came Hurricane Iota, which made landfall as a category 4 storm with 155 mph winds in Nicaragua, just 15 miles from where Eta hit. There is no precedent in the Atlantic for two such powerful hurricanes to make landfall so close together in space and time. Iota brought torrential rains that inundated flooded regions still struggling to recover from Eta, with the combined tolls from the two storms exceeding 300 people dead or missing.

The combined impact of the two hurricanes on Nicaragua was estimated at $738 million – about 6% of that nation’s GDP. But the twin category 4 hurricanes left behind a truly extreme catastrophe in Honduras. As explained in a November 22 article in La Prensa, total damages from Hurricane Eta and Hurricane Iota in Honduras may exceed $10 billion – 40% of the poverty-stricken nation’s GDP. According to the Honduras Foreign Debt Forum (Fodesh), a non-governmental organization dedicated to economic affairs, the twin hurricanes will set Honduras back 22 years in economic development.

Eta and Iota severely affected more than four million people in Honduras, destroyed tens of thousands of houses, damaged or destroyed 110 bridges and 267 roads, and wiped out vast areas of productive farmland. Economic activity in northwestern Honduras’ San Pedro Sula Valley, where 60% of Honduras’s GDP comes from, was devastated. The destruction is expected to drive a large migration of destitute people from Honduras to other nations, including to the U.S.: A November 28 article in El Pais reports that the first caravans of migrants have begun to get organized.

Figure 4. Extreme flooding in Copán Ruinas, Honduras, on November 18, in the aftermath of Hurricane Iota. (Image credit: Xiomara Orellana)

A slew of records

The list of single-season and multi-season records established in 2020 is long. Below are the most notable ones, primarily taken from Dr. Phil Klotzbach’s 2020 season summary from November 30.

Multi-season records

– Fifth consecutive year with above-average Atlantic hurricane activity (previous record: four years, 1998-2001).
– Fifth consecutive year with a category 5 hurricane in the Atlantic (previous record: three years, 2003-2005).

Figure 5. The 2020 Atlantic hurricane season featured six major hurricanes, tied for second highest number of intense hurricanes on record. (Image credit: Tweet by Dakota Smith)

Single-season records
– Thirty named storms (previous record: 28 in 2005).
Five category 4 and stronger hurricanes (tied with 2005, 1999, 1961, and 1933).
– Earliest forming ‘C’ named storm and the earliest named storm formation from the ‘E’ storm onwards.
– Ten named storms formed in September (old record: eight in 2002, 2007 and 2010).
– Five named storms formed in the Caribbean after October 1 (Gamma, Delta, Zeta, Eta and Iota), tying the record set in 2005.
– Four major hurricanes formed in the Atlantic basin after October 1 (Delta, Epsilon, Eta and Iota). Old record: two, set in numerous years.
– November produced 20 named storm days, tied with 1932 for most on record in November.
– Three Atlantic named storms formed in November (Eta, Theta and Iota). This ties 2020 with 1931, 1961, 2001 and 2005 for the most November named storm formations on record.
– Twelve Atlantic named storms made landfall in the continental U.S. (previous record: nine in 1916).
– Six Atlantic hurricanes made landfall in the continental U.S. (tied with 1886 and 1985).
– Five named storms made landfall in Louisiana (previous record: four in 2002).
– Hurricane Laura made landfall with maximum sustained winds of 150 mph in Cameron Parish, Louisiana. Laura is tied with the Last Island Hurricane of 1856 for the strongest winds for a Louisiana hurricane landfall on record.
– Hurricane Eta made landfall in Nicaragua with maximum sustained winds of 140 mph, making it the strongest November landfalling hurricane in Nicaragua on record. That record was broken just 13 days later by Iota, which hit with 155 mph winds.
– Hurricane Iota became a category 5 hurricane on November 16 – the latest Atlantic calendar year category 5 hurricane on record (previous record: November 8, by the Cuba hurricane of 1932).
– Nine named storms rapidly intensified by at least 35 mph in 24 hours in 2020: Hanna, Laura, Sally, Teddy, Delta, Epsilon, Zeta, Eta and Iota. This ties 2020 with 1995 and 2010 for the most rapidly intensifying named storms in a single Atlantic hurricane season on record. Tropical Storm Gamma also met the rapid intensification criteria by intensifying 35 mph in 24 hours, but it was a tropical depression at the start of its rapid intensification phase.
– Three named storm underwent 36-hour intensification of at least 100 mph: Delta, Eta, and Iota. According to an analysis by Sam Lillo, only eight other storms in 169 years of record-keeping accomplished this feat.
– Subtropical Storm Alpha made landfall in Portugal on September 18, becoming the first ever named storm to make landfall in the country. Alpha was also the easternmost-forming named storm on record in the Atlantic. Alpha killed one person in Spain and caused several million dollars (USD) in damages to Portugal and Spain.
– The NOAA Hurricane Hunters flew 86 missions into Atlantic named storms and disturbances, beating the previous record from 2005.

Figure 6. Vertical wind shear during August-September-October over the main development region (MDR) for Atlantic hurricanes, from the Caribbean to the coast of Africa, was at record low levels in 2020, one of the primary reasons for the active 2020 season. (Image credit: Dr. Phil Klotzbach, Colorado State University)

Also see: How climate change is making hurricanes more dangerous

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Posted on December 1, 2020(12:33pm EST).

Jeff Masters

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...

47 replies on “A look back at the horrific 2020 Atlantic hurricane season”

  1. Fiji Meteorological Services
    Tropical Disturbance Summary – 9:00 AM FST December 11 2020
    ==============================================
    North Northwest of Futuna island

    At 21:00 PM UTC, Tropical Disturbance 01F (1004 hPa) located at 12.4S 179.7W is reported as moving west at 8 knots. Position poor based on HIMAWARI-8 infrared and visible imagery.

    Deep convection remains persistent close to the low center and the organization has generally improved over the last 24 hours. Cyclonic circulation extends up to 500HPA. The system is located in a moderate to high sheared environment with a good upper divergence and a low sheared environment just to the northwest of the supposed low level circulation center. Sea surface temperature is around 29-30C.

    Global models have also picked up this system and gradually move it westwards with intensification in next 24 to 48 hours.

    Potential for this disturbance to form into a tropical cyclone in the next 24-48 hours is MODERATE to HIGH.

  2. Mauritius Meteorological Services
    Tropical Cyclone Advisory #20 – 4:00 AM RET December 11 2020
    DEPRESSION RESIDUELLE, EX BONGOYO (03-20202021)
    ==============================================

    East Southeast of Rodrigues island

    At 0:00 AM UTC, Remnant Low Bongoyo (1002 hPa) located at 21.6S 75.3E has 10 minute sustained winds of 30 knots with gusts of 45 knots. The cyclone is reported as moving west at 6 knots.

    Near Gale Force Winds
    =======================
    extending up to 130 nm in the southeastern quadrant and up to 250 nm in the southwestern quadrant

    Dvorak Intensity: T1.5/2.0/W1.0/24 HRS

    Forecast and Intensity
    ========================
    12 HRS 21.1S 73.5E – 30 knots (Depression se Comblant)
    24 HRS 20.6S 70.3E – 30 knots (Depression se Comblant)

    Additional Information
    ==========================
    The convective activity has finally run out of steam in the southern semicircle, Bongoyo is therefore downgraded to a remnant low with maximum winds estimated at 30 kts in the southern semi-circle.

    Since 1800z, the system seems to have resumed its expected westward movement according to the still uncertain night fix. The filled-up low will thus continue on a general westward track over the next 48 hours, on the northern edge of the subtropical high, before evolving into a low levels trough beyond.

    There is no significant impact to be expected in terms of wind and rain on the inhabited lands of the Mascarene islands.

    This is the last advisory from RSMC Reunion

  3. Mauritius Meteorological Services
    Tropical Cyclone Advisory #17 – 10:00 AM RET December 10 2020
    TEMPETE TROPICALE MODEREE BONGOYO (03-20202021)
    ==============================================

    East of Rodrigues island

    At 6:00 AM UTC, Moderate Tropical Storm Bongoyo (996 hPa) located at 21.4S 75.5E has 10 minute sustained winds of 40 knots with gusts of 55 knots. The cyclone is reported as moving southwest at 5 knots.

    Gale Force Winds
    ===============
    Extending up to 50 nm in the western semi-circle

    Near Gale Force Winds
    =======================
    70 nm radius from the center, extending up to 90 nm in the southwestern quadrant and up to 100 nm in the southeastern quadrant

    Dvorak Intensity: T2.5/3.0/W0.5/12 HRS

    Forecast and Intensity
    ========================
    12 HRS 21.3S 74.4E – 35 knots (Tempête Tropicale Modérée)
    24 HRS 21.0S 72.3E – 30 knots (Depression se Comblant)
    48 HRS 20.8S 65.7E – 30 knots (Depression Residuelle)

    Additional Information
    ==========================
    Not surprises in the last 6 hours, Bongoyo’s environmental conditions continue to degrade its cloud pattern. The 0340utc ASCAT swath shows a lengthening circulation with a center that is difficult to locate but placing it at the northwestern edge of the sheared convective mass. Winds of 40 kts are still noticeable in Bongoyo’s western semi-circle.

    Bongoyo begins its westward track by gradually accelerating in contact with subtropical high pressures. This is explained by the weakening of the system, which leads to a lowering of the steering flow at the lower levels. Some uncertainty persists, however, on the speed of the western flow, leaving differences in timing between the most recent guidance of around 6 hours.

    With no risk of intensification, the system is gradually taking on a very attenuated form. Given the current forecast track, the Bongoyo remnant low should not have a significant impact in terms of wind and rain on the mascarene inhabited lands.

  4. Tropical Cyclone Warning Center Perth
    Tropical Cyclone Outlook – 2:00 PM WST December 9 2020
    ========================================

    At 1PM WST, Tropical Low 02U was located near 14.7S 112.0E, over open waters approximately 800 kilometers southeast of Christmas Island and 900 kilometers northwest of Karratha. The system is accelerating towards the southeast and is forecast to cross the east Pilbara coast during Friday, most likely during the afternoon.

    There is a Low risk of 02U developing into a tropical cyclone overnight into Friday morning prior to crossing the east Pilbara coast. There is a very slight risk it moves slower than forecast and crosses the coast as late as Saturday morning. Although the risk of the system being classified as a tropical cyclone is Low, there is a moderate to high risk of persistent gale force winds in the northeastern quadrant of 02U, meaning damaging winds could still be experienced near the low. These stronger winds are the result of enhanced monsoonal northwesterly flow and the system’s speed of movement. Heavy rainfall is also expected with the passage of the tropical low.

  5. Fiji Meteorological Services
    Tropical Disturbance Summary – 9:00 AM FST December 10 2020
    ==============================================
    northeast of Futuna island

    At 21:00 PM UTC, Tropical Disturbance 01F (1004 hPa) located at 12.6S 176.3W is reported as moving west at 6 knots. Position poor based on HIMAWARI-8 visible imagery.

    Deep convection remains persistent to the northeast of the supposed low level circulation center and organization remains poor. Cyclonic circulation extends up to 500HPA. The system is located to the west of an upper trough in a moderate to high sheared environment. Sea surface temperature is around 29C.

    To the west of the system are areas of low wind shear and good out flow which are favorable for cyclone formation. The system is expected to continue westwards over this favorable conditions and expected to gradually intensify.

    Global models have also picked up this system and gradually move it westwards with slight intensification.

    Potential for this disturbance to form into a tropical cyclone in the next 24-48 hours is MODERATE.

  6. Mauritius Meteorological Services
    Tropical Cyclone Advisory #16 – 4:00 AM RET December 10 2020
    TEMPETE TROPICALE MODEREE BONGOYO (03-20202021)
    ==============================================

    East of Rodrigues island

    At 0:00 AM UTC, Moderate Tropical Storm Bongoyo (992 hPa) located at 19.7S 76.3E has 10 minute sustained winds of 40 knots with gusts of 60 knots. The cyclone is reported as moving west southwest at 3 knots.

    Gale Force Winds
    ===============
    Extending up to 60 nm in the eastern semi-circle and up to 90 nm in the southwestern quadrant

    Near Gale Force Winds
    =======================
    50 nm radius from the center, extending up to 140 nm in the southwestern quadrant and up to 180 nm in the southeastern quadrant

    Dvorak Intensity: T2.5/3.0/W1.0/12 HRS

    Forecast and Intensity
    ========================
    12 HRS 21.0S 74.2E – 35 knots (Tempête Tropicale Modérée)
    24 HRS 20.9S 72.5E – 30 knots (Depression Residuelle)
    48 HRS 20.8S 66.8E – 30 knots (Depression Residuelle)
    72 HRS 20.2S 60.8E – 25 knots (Depression se Dissipant)

    Additional Information
    ==========================
    Bongoyo’s structure keeps on deteriorating within unfavorable environmental conditions. 2219z SSMI image reveals that the circulation shows signs of elongation, with deep convection only triggering within the southern semi-circle.

    Bongoyo has been slowing down since the last hours and should resume a westward movement, gradually accelerating in contact with the subtropical high pressure. This is explained by the weakening of the system which leads to a lowering of the steering flow. However, some differences concerning the timing of this westward acceleration have emerged among the most recent guidance. This suggests a moderate along-track uncertainty.

    In a very attenuated form thereafter and given the current projected track, the remnant of Bongoyo should not have a significant impact in terms of wind and rain on the inhabited lands.

  7. Fiji Meteorological Services
    Tropical Disturbance Summary – 9:00 AM FST December 9 2020
    ==============================================
    North of Samoa

    At 21:00 PM UTC, Tropical Disturbance 01F (1005 hPa) located at 12.0S 172.7W is reported as slowly moving. Position poor based on HIMAWARI-8 infrared imagery.

    Deep convection remains persistent to the north and east of the supposed low level circulation center and organization has slightly improve. Cyclonic circulation extends up to 700HPA. The system is located under good diffluent area with good outflow to the north and east of the system. System lies in a low sheared environment. Sea surface temperature is around 29C.

    Global models have picked up this system and gradually move it westwards with slight intensification.

    Potential for this disturbance to form into a tropical cyclone in the next 24-48 hours is LOW to MODERATE.

  8. Mauritius Meteorological Services
    Tropical Cyclone Advisory #11 – 22:00 PM RET December 8 2020
    FORTE TEMPETE TROPICAL BONGOYO (03-20202021)
    ==============================================

    East Northeast of Rodrigues island

    At 18:00 PM UTC, Severe Tropical Storm Bongoyo (988 hPa) located at 18.5S 76.7E has 10 minute sustained winds of 55 knots with gusts of 75 knots. The cyclone is reported as moving west southwest at 12 knots.

    Storm Force Winds
    ==================
    Extending up to 25 nm in the southern semi-circle and the northeastern quadrant

    Gale Force Winds
    ===============
    30 nm from the center, extending up to 50 nm in the southern semi-circle

    Near Gale Force Winds
    =======================
    50 nm radius from the centre, extending up to 80 nm in the southwestern quadrant and up to 100 nm in the southeastern quadrant

    Dvorak Intensity: T3.5/3.5/S0.0/6 HRS

    Forecast and Intensity
    ========================
    12 HRS 19.7S 75.9E – 50 knots (Forte Tempête Tropicale)
    24 HRS 20.2S 75.4E – 40 knots (Tempête Tropicale Modérée)
    48 HRS 20.3S 71.9E – 30 knots (Depression Residuelle)
    72 HRS 20.8S 66.3E – 25 knots (Depression Residuelle)

    Additional Information
    ==========================
    In the last 6 hours, convective activity maintained near Bongoyo center. Microwave images (especially 1312z SSMIS) show that deep convection is still concentrated in the southwestern semicircle of the system. This asymmetry is probably related to the mid-tropospheric shear analyzed by CIMSS around 20 kts from north. The latest smap and ASCAT passes show little evolution compared to those of 12 hours ago. The intensity is thus maintained at 55 kts.

    Bongoyo seems at the end of its deepening phase as the favorable conditions windows is closing in. Indeed, the deep vertical shear should increase rapidly in the next hours and be associated with more efficient dry intrusions. With a rapidly diluting warm core, the system is thus expected to gradually weaken into a residual depression.

    Under the influence of the mid-level subtropical ridge, the storm should keep on heading southwestward over the next hours. Tomorrow, the steering flow should come down to lower levels due to the weakened state of the system. Bongoyo is thus expected to drift generally westward on the northern side of the subtropical high pressure area.

    Under a very attenuated form this weekend, the residual low Bongoyo should not have a significant impact in terms of wind and rainfall over the inhabited islands.

  9. Fiji Meteorological Services
    Tropical Disturbance Summary – 18:00 PM FST December 8 2020
    ==============================================
    Near Samoan islands

    At 6:00 AM UTC, Tropical Disturbance 01F (1005 hPa) located at 12.9S 170.8W is reported as slowly moving. Position poor based on HIMAWARI-8 infrared imagery.

    Deep convection remains persistent to the north and east of the supposed low level circulation center and remains poorly organized. Cyclonic circulation extends up to 700HPA. The system is located under good divergent area with good outflow to the north and east of the system. System lies in a low sheared environment. Sea surface temperature is around 29C.

    Global models have picked up this system and gradually move it westwards with slight intensification.

  10. Mauritius Meteorological Services
    Tropical Cyclone Advisory #10 – 16:00 PM RET December 8 2020
    FORTE TEMPETE TROPICAL BONGOYO (03-20202021)
    ==============================================

    East Northeast of Rodrigues island

    At 12:00 PM UTC, Severe Tropical Storm Bongoyo (988 hPa) located at 17.7S 77.7E has 10 minute sustained winds of 55 knots with gusts of 80 knots. The cyclone is reported as moving southwest at 11 knots.

    Storm Force Winds
    ==================
    Extending up to 25 nm in the southwestern quadrant and up to 30 nm in the southeastern quadrant

    Gale Force Winds
    ===============
    20 nm radius from the centre, extending up to 30 nm in the northwestern quadrant, up to 60 nm in the southwestern quadrant and up to 90 nm in the southeastern quadrant

    Near Gale Force Winds
    =======================
    50 nm radius from the centre, extending up to 175 nm in the southern semi-circle

    Dvorak Intensity: T3.5/4.0/W0.5/6 HRS

    Forecast and Intensity
    ========================
    12 HRS 19.8S 76.9E – 50 knots (Forte Tempête Tropicale)
    24 HRS 20.5S 75.7E – 40 knots (Tempête Tropicale Modérée)
    48 HRS 20.4S 73.2E – 30 knots (Depression se Comblant)
    72 HRS 20.5S 68.0E – 25 knots (Depression Residuelle)

    Additional Information
    ==========================
    Over the last 6 hours, Bongoyo showed signs of resistance against the moderate northwesterly mid-level wind shear. Indeed, strong convective bursts are located near the center, in the western semi-cercle on the 1126z microwave SSMIS image. The mid-level eye has lost its definition and is now opened on the eastern side.

    The window for intensification is gradually closing today, with the strengthening of a northerly to northwesterly shear constraint in the mid-levels. This already limits the development of the system today. Tomorrow Wednesday, deep layer shear should also increase and be associated to more efficient dry intrusions. With a rapidly diluting warm core, the system is thus expected to gradually weaken into a residual depression.

    Under the influence of the mid-level subtropical ridge, the storm should keep on heading southwestward over the next hours. Tomorrow, the steering flow should come down to lower levels due to the weakened state of the system. Bongoyo is thus expected to drift generally westward on the northern side of the subtropical high pressure area.

    Under a very attenuated form this weekend, the residual low Bongoyo should not have a significant impact in terms of wind and rainfall over the inhabited islands.

  11. Mauritius Meteorological Services
    Tropical Cyclone Advisory #9 – 10:00 AM RET December 8 2020
    FORTE TEMPETE TROPICAL BONGOYO (03-20202021)
    ==============================================

    East Northeast of Rodrigues island

    At 6:00 AM UTC, Severe Tropical Storm Bongoyo (988 hPa) located at 17.0S 78.2E has 10 minute sustained winds of 55 knots with gusts of 80 knots. The cyclone is reported as moving southwest at 11 knots.

    Storm Force Winds
    ==================
    extending up to 25 nm in the southwestern quadrant and up to 30 nm in the southeastern quadrant

    Gale Force Winds
    ===============
    20 nm radius from the center, extending up to 30 nm in the northwestern quadrant, up to 60 nm in the southwestern quadrant and up to 90 nm in the southeastern quadrant

    Near Gale Force Winds
    =======================
    50 nm radius from the center, extending up to 175 nm in the southern semi-circle

    Dvorak Intensity: T4.0/4.0/D1.5/24 HRS

    Forecast and Intensity
    ========================
    12 HRS 18.4S 77.1E – 60 knots (Forte Tempête Tropicale)
    24 HRS 20.0S 76.5E – 55 knots (Forte Tempête Tropicale)
    48 HRS 20.8S 74.6E – 40 knots (Tempête Tropicale Modérée)
    72 HRS 21.4S 70.1E – 30 knots (Depression se Comblant)

    Additional Information
    ==========================
    Over the last 6 hours, some strong convective bursts maintained near the circulation center, located on the southeastern border of the main convection. 2249z and 0034z 89ghz SSMIS images showed a well-defined mid-level eye. Thus, in agreement with available subjective and objectives estimates, Bongoyo has been upgraded to the severe tropical storm stage. However, the 89ghz microwave image from the 0354z METOP-B swath showed that the eastern semi-circle of the mid-level core already began to be eroded by dry air. Despite the emergence of an ill-defined and veiled eye on the visible imagery, the influence of dry air is also visible.

    The window for intensification is gradually closing today, with the strengthening northerly to northwesterly shear constraint in the mid-levels. This should limit the development of the system today, even if the tropical cyclone stage might still be reached by tonight. Tomorrow Wednesday, deep layer shear should also increase and be associated to more efficient dry intrusions. The system is thus expected to gradually weaken into a residual depression.

    Under the influence of the mid-level subtropical ridge, the storm should keep on heading southwestward. Bongoyo’s track forecast is a little bit more located in the south, in coherence with the stronger analyzed intensity which allows the storm to remain longer under the ridge influence. From Thursday, the steering flow should come down to lower levels due to the weakened state of the system. Bongoyo is thus expected to drift generally westward on the northern side of the subtropical high pressure area.

    Under a very attenuated form this weekend, the residual low Bongoyo should not have a significant impact in terms of wind and rainfall over the inhabited islands.

  12. Mauritius Meteorological Services
    Tropical Cyclone Advisory #8 – 4:00 AM RET December 8 2020
    TEMPETE TROPICAL MODEREE BONGOYO (03-20202021)
    ==============================================

    East Northeast of Rodrigues island

    At 0:00 AM UTC, Moderate Tropical Storm Bongoyo (992 hPa) located at 15.9S 78.8E has 10 minute sustained winds of 45 knots with gusts of 65 knots. The cyclone is reported as moving west southwest at 11 knots.

    Gale Force Winds
    ===============
    extending up to 50 nm in the southeastern quadrant and up to 100 nm in the southwestern quadrant

    Near Gale Force Winds
    =======================
    40 nm radius from the center, extending up to 150 nm in the southeastern quadrant and up to 180 nm in the southwestern quadrant

    Dvorak Intensity: T3.5/3.5/D0.5/6 HRS

    Forecast and Intensity
    ========================
    12 HRS 17.4S 77.2E – 50 knots (Forte Tempête Tropicale)
    24 HRS 18.8S 76.5E – 45 knots (Tempête Tropicale Modérée)
    48 HRS 20.0S 74.9E – 35 knots (Tempête Tropicale Modérée)
    72 HRS 20.0S 71.2E – 25 knots (Depression se Comblant)

    Additional Information
    ==========================
    During the period 0000 and 0600 utc, the cloud configuration of Bongoyo in central dense overcast was maintained while the convection band further east is well detached. In this configuration reflecting an intensification compared to the previous period, the Dvorak analysis leaves however Bongoyo at the upper limit of moderate tropical storm with estimated winds of about 45 kts, mainly in the southern sector of the system. The threshold of strong tropical storm is soon.

    Bongoyo’s track forecasting shows a slightly more marked southward descent than initially. With first of all, a southwestward maintenance under the influence of the subtropical ridge. Then with the passage further south of a trough, the subtropical ridge induces a less marked directional flow: the track slows down and takes a more marked meridional component in mid Tuesday which persists a little longer. In mid-week, a new subtropical ridge is positioned southwest of Bongoya imposing again a westward track which accelerates.

    The favorable intensification window ends on Tuesday, with the strengthening of the mid-tropical wind shear. This constraint limits the development of the system today and then on Wednesday, the deep vertical wind shear should also increase and be associated with more important dry intrusions. The system should then rapidly evolve into a remnant low during its move towards the Mascarene.

  13. Mauritius Meteorological Services
    Tropical Cyclone Advisory #6 – 16:00 PM RET December 7 2020
    TEMPETE TROPICAL MODEREE BONGOYO (03-20202021)
    ==============================================

    Southeast of Diego Garcia
    East Northeast of Rodrigues island

    At 12:00 PM UTC, Moderate Tropical Storm Bongoyo (995 hPa) located at 15.1S 81.0E has 10 minute sustained winds of 40 knots with gusts of 60 knots. The cyclone is reported as moving west southwest at 11 knots.

    Gale Force Winds
    ===============
    extending up to 40 nm in the southern semi-circle and the northeastern quadrant

    Near Gale Force Winds
    =======================
    30 nm radius from the center, extending up to 50 nm in the northeastern quadrant, up to 130 nm in the southwestern quadrant, and up to 145 nm in the southeastern quadrant

    Dvorak Intensity: T2.0/2.5/W0.5/6 HRS

    Forecast and Intensity
    ========================
    12 HRS 16.2S 78.8E – 40 knots (Tempête Tropicale Modérée)
    24 HRS 17.5S 77.2E – 40 knots (Tempête Tropicale Modérée)
    48 HRS 18.9S 75.9E – 35 knots (Tempête Tropicale Modérée)
    72 HRS 19.4S 72.4E – 25 knots (Depression se Comblant)

    Additional Information
    ==========================
    Since 0600z, after a first improvement phase, Bongoyo cloud pattern has started to decay. The convective activity near the center is concentrated in the southwest quadrant. The gmi pass of 0750z also shows a small weakness in the northwest quadrant. Convection in 89ghz also appears fragmented. These elements suggest that the northwestern mid shear may have begun to strengthen. It is analyzed around 15 kts by the CIMSS at 0900z. The intensity has been increased and maintained at 40 kts to take into account the evolution at the beginning associated with a certain inertia.

    Little change in the track forecast philosophy : Bongoyo continued it southwestward track under the influence of the subtropical ridge further south. With the passage further south of a trough, the low slows down from tomorrow and take a more marked meridian component. From mid-week, the return of the subtropical ridge imposes again a westward track while accelerating.

    Along this track, Bongoyo seems at the end of its favorable phase with the reinforcement of the mid troposphere shear. It should limit the development of the system. On Wednesday, deep vertical shear should also increase and be associated with more important dry mid-troposphere intrusions. The system should then rapidly evolve into a residual depression.

    No threat is forecast for the inhabited lands.

  14. At last, the Moon rises over Costa Rica
    A perfect half moon with its equator breathlessly horizontal
    Wynken, Blynken and Nod one night sailed off in a wooden shoe….

    This may be the first Moonrise I’ve seen from this location in the almost 18th months I’ve lived and sheltered here in the cloudforests of Monteverde. Most of the forests have been “cleared” in CR, so there are plenty of other “improved” views.

    Sssshh.

    Thank you Jeff and Bob for all you do. I’m making good progress sharing the Fram Dam, key to halting the pop of the Anthropocene bubble splattering into the Anthropocene Extinction…we might have time to plant and mature three trillion trees and thus reverse this sorry failure of human civilization. Earth, where men eat while children starve. Numbers don’t lie. We might not make it…but if not, then it’s good to know that isn’t because God is against us. She gave us a way forward to the best of all possible worlds, and we are failing because this is what we became, practicing at every meal….

  15. Mauritius Meteorological Services
    Tropical Cyclone Advisory #5 – 10:30 AM RET December 7 2020
    TEMPETE TROPICAL MODEREE BONGOYO (03-20202021)
    ==============================================

    Southeast of Diego Garcia
    East Northeast of Rodrigues island

    At 6:00 AM UTC, Moderate Tropical Storm Bongoyo (996 hPa) located at 14.6S 82.1E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as moving west southwest at 12 knots.

    Gale Force Winds
    ===============
    40 nm from the center in southern semi-circle

    Near Gale Force Winds
    =======================
    30 nm radius from the center, extending up to 130 nm from the southwestern quadrant and up to 145 nm in the southeastern quadrant

    Dvorak Intensity: T2.5/2.5/D 1.0/24 HRS

    Forecast and Intensity
    ========================
    12 HRS 15.4S 80.2E – 40 knots (Tempête Tropicale Modérée)
    24 HRS 16.4S 78.3E – 40 knots (Tempête Tropicale Modérée)
    48 HRS 19.0S 76.4E – 35 knots (Tempête Tropicale Modérée)
    72 HRS 19.2S 74.2E – 25 knots (Depression se Comblant)

    Additional Information
    ==========================
    Since 0000z, 03 cloud pattern has significantly improved with a curved band now wrapping around the center of more than a semi-circle. However cloud tops warmed up since then. Given this evolution and the microwave passes of the end of the night (0050z SSMIS), the system has been named Bongoyo by the Mauritian Services. The 0414z ASCAT pass confirmed the presence of gale force winds in the southern semi-circle.

    Little change in the track forecast philosophy : Bongoyo has resumed a west southwest trajectory due to the influence of the subtropical ridge further south. With the passage further south of a Talweg, the low slows down from tomorrow by taking a more marked meridian component. From mid-week, the return of the subtropical ridge imposes again a westward track while accelerating.

    Along this track, Bongoyo will benefit from a favorable window during the next 12 hours. Next night, the reinforcement of a moderate northwesterly constraint in the middle troposphere should limit the development of the system. On Wednesday, deep vertical shear should also increase and be associated with dry mid-troposphere intrusions. The system should then rapidly evolve into a residual depression.

    No threat is envisaged for the inhabited lands.

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