NC National Guard
Members of the North Carolina National Guard wear face masks as they support local first responders near Windsor, North Carolina, in the aftermath of Hurricane Isaias (Photo credit: NCNG / Flickr)

 

August 5 update:

Hurricane Isaias roared into Canada and became post-tropical on Tuesday night, ending a long rampage that left behind an unusually high amount of destruction for a category 1 hurricane.

Isaias killed six people – two in the Dominican Republic, two from a tornado in North Carolina, one from a falling tree in New York City, and one from a falling tree in Maryland. Isaias brought multiple wind gusts over 70 mph to the mid-Atlantic states and North Carolina, and the storm’s strong winds and heavy rains caused over five million customers to lose power. Isaias drove a record storm tide to Wilmington, North Carolina, and the third-highest storm tide on record to Myrtle Beach, South Carolina. Total damage from Isaias is likely to be over a billion dollars, and its impact makes it a candidate to have its name retired from the Atlantic list of storms at the conclusion of the season.

Figure 1
Figure 1. Peak wind gusts from Isaias. (Image credit: National Weather Service Eastern Region)

Isaias’s powerful winds cause over 6.8 million customers to lose power

The peak wind gust from Isaias was recorded on top of New Hampshire’s Mt. Washington, which observed its highest gust on record for the month of August: 147 mph. At sea level, the highest gusts in the northeast U.S. occurred on New York’s Long Island, where four stations recorded gusts of 73 mph or more, including a 78-mph gust at Farmingdale Airport. The storm generated a number of gusts over 70 mph along Chesapeake Bay and Delaware Bay, as well as along the coast of North Carolina where Isaias made landfall as a category 1 hurricane with 85 mph winds at 11:10 p.m. EDT August 3, 2020. Other strong gusts from Isaias in the New York City area included:

78 mph New York City’s Battery Park;
73 mph Jackson Heights in Queens County;
70 mph NYC Kennedy Airport; and
69 mph NYC LaGuardia Airport.

Figure 2
Figure 2. Radar image of Tropical Storm Isaias over New Jersey at 12:02 p.m. EDT Tuesday, August 4, 2020. A few hours after this image was taken, the New York City area experienced multiple wind gusts of more than 70 mph. (Image credit: National Weather Service via Mark Nissenbaum/Florida State University)

Isaias’s powerful winds led to one of the largest power outage events ever recorded for a category 1 hurricane. From power outage reports tweeted out by poweroutage.us during the event, here were the peak number of customers affected in each state and one Canadian province:

New Jersey 1,379,000
New York 811,000
Connecticut: 725,000
Pennsylvania: 371,000
North Carolina: 349,000
Virginia: 337,000
Massachusetts: 218,000
Rhode Island: 129,000
Maryland: 110,000
New Hampshire: 74,000
Maine: 72,000
Delaware: 51,000
Quebec: 38,000
Vermont: 20,000

In addition, 400,000 customers in Puerto Rico lost power during the height of the tropical storm. The true number of power outages in each state was higher, since power restoration efforts were ongoing during the event, and these snapshots did not capture the peak power outages for each state. Poweroutages.us tweeted that more than 6.4 million customers from /South Carolina to Maine los power during Isaias. When combined with the 400,000 customers who lost power in Puerto Rico, the tally comes to more than 6.8 million customers in the U.S. who lost power.

Poweroutage.us lists just one other weather event since 2016 that has caused a larger power outage. Here are the four events since 2016 that have knocked out power to at least 2 million customers:

Hurricane Irma, Sep 9 – 11, 2017: 7.6 million
Hurricane Isaias, August 4, 2020: 6.8 million
Hurricane Michael, Oct 10 – 12, 2018: 3.1 million
Severe thunderstorms, July 19 – 23, 2019: 2.8 million

Over the years, I’ve put together a non-comprehensive list of power outages from natural disasters in the U.S., using various official and unofficial sources. Here is my list of the largest weather-related power outages in U.S. history:

Blizzard of March 1993 “Superstorm”: 10 million
Hurricane Sandy, October 2012: 8 million
Hurricane Irene, August 2011: 7.5 million
Hurricane Ike, September 2008: 7.5 million
Hurricane Isaias, August 2020: 6.8 million
Hurricane Frances, September 2004: 6 million
Hurricane Isabel, September 2003: 6 million
Mid-Atlantic Derecho, 2012: 4.2 million

Figure 3
Figure 3. The history of high-water levels (storm tide) in Wilmington, North Carolina since 1935. Data from the site is plotted up only to mid-2018; purple dots have been added to show the two record-setting storm tides from Hurricane Florence (2018) and Hurricane Isaias (2020). Note that the level of Mean Higher High Water (MHHW) in Wilmington has risen by 13 inches since 1935. The red line marks a water level that has a 1% chance of occurring per year: a 1-in-100-year event. Wilmington has had three 1-in-100-year events in the past five years—an occurrence made more likely as sea level rises because of human-caused climate change. (Image credit: NOAA Tides and Currents)

Wilmington has its third 1-in-100-year storm surge flood in past five years

Isaias’s landfall near the South Carolina-North Carolina border coincided with high tide, resulting in some of the highest coastal water levels ever measured there. Water levels in Wilmington, North Carolina, on the Cape Fear River set an all-time record: 4.19 feet above Mean Higher High Water (MHHW), beating the record of 3.6 feet above MHHW set on September 14, 2018, during Hurricane Florence. Data extend back to 1935 at the site.

Remarkably, the site has experienced three 1-in-100-year storm surge events in the past five years – Hurricane Isaias in 2020, Hurricane Florence in 2018, and Hurricane Matthew in 2016. All three hurricanes broke the previous record.

The tide gauge at Springmaid Pier in Myrtle Beach, South Carolina, recorded its third-highest water level on record from Isaias on August 3, behind only the storm tides from Hurricane Hugo of 1989 and Hurricane Matthew of 2016. The water inundated the Family Kingdom Amusement Park in Myrtle Beach.

As tweeted by meteorologist Bob Henson, the storm surge from Isaias at New York City’s Battery Park hit 4.49 feet on August 4 – higher than that of Hurricane Irene in 2011 (4.36 feet). Fortunately, Isaias’s surge peaked near low tide. Had the peak storm surge arrived at high tide, damaging storm surge flooding would have occurred in the city, perhaps comparable to that of Hurricane Irene.

Figure 4
Figure 4. Observed 48-hour rainfall from Isaias ending at 8 p.m. EDT August 4, 2020. (Image credit: National Weather Service Eastern Region)

Isaias’ heavy rains bring record river flooding at five gauges

Isaias dumped two to 10 inches of rain along a swath from South Carolina to Canada, resulting in mostly minor to moderate river flooding. However, major flooding was observed along some rivers in the mid-Atlantic, and three river gauges in eastern Pennsylvania, one in northern Delaware, and one in Maryland set all-time flood records during the storm:

Perkiomen Creek at Graterford, Pennsylvania (records going back to at least 1933);
Little Lehigh Creek near Allentown, Pennsylvania (records going back to at least 1935);
Jordan Creek at Allentown, Pennsylvania (records going back to at least 1955);
Christina River at Coochs Bridge, Delaware (records going back to at least 1947); and
St. Clement Creek near Clements, Maryland (records going back to at least 1972).

A large and severe tornado outbreak

The powerful jet stream that Isaias was embedded in during its passage up the coast helped the hurricane spawn an unusually large and severe tornado outbreak for a tropical cyclone. And get this: An EF3 tornado touched down in North Carolina–one of only 43 tornadoes of at least EF3 strength ever recorded in association with a tropical cyclone. [This paragraph updated at 10:25 a.m. EDT on August 6.]

In addition, at least 32 preliminary tornado reports were logged by NOAA’s Storm Prediction Center August 3 – 4. A tornado caused major damage at a community of manufactured homes in Bertie County, North Carolina, where two people were killed and 20 injured. An EF2 tornado caused major damage in Courtland, Virginia, and EF0 and EF1 tornadoes hit downtown Suffolk, Virginia. Another apparent twister led to two injuries and significant structural damage in White Stone, Virginia, and another caused damage Tuesday morning near Delaware’s capital city of Dover. All told, it appears that Isaias brought one of the largest known tornado outbreaks ever recorded on the Delmarva Peninsula.

Isaias the season’s earliest ‘I’ storm and earliest fifth U.S. landfall

Isaias set a record for the Atlantic hurricane season’s earliest formation of an “I” storm. Isaias’s formation date of July 30 (Greenwich time) came nearly a week earlier than the previous earliest appearance of the Atlantic’s ninth storm of the year, Irene on August 5, 2005.

Isaias was also the fifth named storm to make landfall in the U.S. this year, setting a record for the earliest in the season that a fifth storm has made a U.S. landfall. The previous record came on August 18, 1916. That season also holds the record for most U.S. landfalls in one year, with nine.

Figure 5
Figure 5. Visible GOES-16 satellite image of 94L at 11:50 a.m. EDT Wednesday, August 5, 2020. (Image credit: NOAA/RAMMB)

Next system to watch: 94L

A small low-pressure system, designated 94L by the National Hurricane Center, was located about 300 miles west-southwest of Bermuda at noon EDT Wednesday, and was drifting southwest. Satellite images showed that 94L had developed a well-defined surface circulation, but its heavy thunderstorm activity was extremely limited.
Though 94L was in an area with light wind shear of 5 – 10 knots, the system was embedded in a very dry atmosphere with a mid-level relative humidity of 45%, which was squelching development. Weak steering currents will result in a slow and erratic motion for 94L this week. Late in the week, wind shear is predicted to rise, and the atmosphere will remain dry, making development unlikely.

In an 8 a.m. EDT Tuesday Tropical Weather Outlook, NHC gave 94L two-day and five-day odds of formation of 10%. The system has very weak model support for development, and does not appear to be a threat to any land areas over the next five days.

The next name on the Atlantic list of storms is Josephine. The current record for earliest 10th Atlantic named storm formation is August 22, 2005, when Jose formed.

A quiet period in the Atlantic coming

The top three reliable models for predicting hurricane genesis are not calling for any new Atlantic tropical cyclones to develop during the coming week. The suppressed phase of an atmospheric disturbance called a Convectively Coupled Kelvin Wave will be passing over the Atlantic during the coming week, bringing sinking air that favors higher surface pressures and reduced chances of tropical cyclone formation (see tweets by IBM’s Michael Ventrice and NOAA’s Andy Hazleton).

The coming quiet may be the proverbial calm before the storm. The August 5, 2020 seasonal forecast from Colorado State University is calling for an additional 15 named storms in the Atlantic this season, with ten of them hurricanes and five of them major hurricanes. If this forecast verifies, we’ll run out of names in the Atlantic and start using Greek names again, as has only happened once—during the 2005 hurricane season.

This will be the last post on the tropics this week unless there is a significant change in the forecast.


Post Update on 8/4

Isaias landfall on radar
Radar image of Hurricane Isaias at landfall near the South Carolina-North Carolina border at 11:10 p.m. EDT Monday, August 3, 2020. (Image credit: National Weather Service via Mark Nissenbaum/Florida State University)

Hurricane Isaias made landfall in southern North Carolina around 11:10 p.m. EDT Monday, August 3, 3020, near Ocean Isle Beach, with maximum sustained winds of 85 mph and a central pressure of 988 mb. Near the time of landfall, sustained category 1 hurricane force winds of 76 mph, gusting to 87 mph, were observed at Oak Island, North Carolina.

According to tweets by storm chaser Jeff Piotrowski, the situation on Oak Island was intense during landfall, with multiple building fires, damaged roofs, and a dangerous storm surge forcing people to shelter in upper stories. Drone video taken on Oak Island Tuesday morning showed extensive overwash of sand on roads and storm surge damage to vehicles and first stories of buildings.

Figure 1
Figure 1. Water levels in Wilmington, North Carolina, on the Cape Fear River during the passage of Hurricane Isaias set an all-time record. (Image credit: NOAA)

A record storm surge in Wilmington, North Carolina

Isaias’s landfall near the South Carolina-North Carolina border coincided with high tide, resulting in some of the highest coastal water levels ever measured there. Water levels in Wilmington, North Carolina, on the Cape Fear River set an all-time record Monday night, beating the record set on September 14, 2018, during Hurricane Florence. Data extend back to 1935 at the site. Drone footage showed considerable damage at one marina in the city.

The tide gauge at Springmaid Pier in Myrtle Beach, South Carolina, recorded its third-highest water level on record Monday evening, behind only Hurricane Hugo of 1989 and Hurricane Matthew of 2016. The water inundated the Family Kingdom Amusement Park in Myrtle Beach.

Figure 2
Figure 2. View at 8:15 p.m. EDT August 3, 2020, from Frying Pan Tower, a surplus Coast Guard Light tower located 34 miles off the coast of Cape Fear, North Carolina. At the time, Hurricane Isaias was generating tropical storm-force winds of 40 mph at the site. (Image credit: explore.org)

Record earliest fifth U.S. landfall by a named storm

Isaias was the fifth named storm to make landfall in the U.S. this year, setting a record for the earliest in the season that a fifth storm has made a U.S. landfall. Here are the other Atlantic named storms in 2020 to hit the U.S., along with their preliminary damage estimates from insurance broker Aon and other sources:

  • Hurricane Hanna in South Texas on July 25 (90 mph winds, $500+ million in damage to the U.S. and Mexico)
  • Tropical Storm Fay in New Jersey on July 10 (50 mph winds, six deaths, $350 million in damage)
  • Tropical Storm Cristobal in Louisiana on June 7 (50 mph winds, one death, $325 million in damage)
  • Tropical Storm Bertha in South Carolina on May 27 (50 mph winds, $200 million in damage)

The previous record-earliest U.S. landfall by the fifth named storm of the season was on August 18, 1916. That season also holds the record for most U.S. landfalls in one year, with nine; second place is jointly held by 2005, 2004, and 1985, with eight. Two other Atlantic hurricane seasons have recorded five U.S. landfalls by August: 1886 (on August 20) and 1936 (on August 31). During the period 1851 – 2019, the U.S. averaged 3.2 named storm landfalls per year, 1.6 hurricane landfalls, and 0.5 major hurricane landfalls. Thanks go to Dr. Phil Klotzbach of Colorado State for these stats. According to Klotzbach, Isaias’s landfall as a hurricane in North Carolina makes 2020 the fifth consecutive Atlantic hurricane season with two or more landfalling hurricanes in the continental United States. From 2009 through 2015, no season had more than one landfalling continental U.S. hurricane.

Figure 3
Figure 3. Visible GOES-17 satellite image of Tropical Storm Isaias at 11 a.m. EDT Tuesday, August 4, 2020. (Image credit: NOAA/RAMMB)

Isaias speeding into the northeast U.S.

At 11 a.m. EDT Tuesday, August 4, 2020, Isaias was just below hurricane strength, with top sustained winds of 70 mph, and was speeding north-northeast at 35 mph into the northeast U.S. A strong cold front and jet stream to Isaias’s west was allowing the storm to maintain its strength unusually far north, even with the center of the storm over land. Isaias is expected to lose its tropical characteristics on Wednesday morning, when it will be in Canada, north of Maine.

Isaias was generating damaging wind gusts along its path, with Manteo, North Carolina, Norfolk, Virginia, Salisbury, Maryland, and Atlantic City, New Jersey, all recording wind gusts over 60 mph Tuesday morning. Shortly before 1 p.m. EDT on Tuesday, gusts of 52 mph at Newark International Airport and 53 mph at John F. Kennedy International Airport in New York City were reported. The National Hurricane Center also reported that a wind gust of 94 mph was measured at a weather station at York River East, Virginia.

Isaias’s high winds and heavy rains caused massive power outages along the eastern seaboard, with nearly 2 million customers losing power Tuesday morning. At 8 a.m. EDT Tuesday, NC Emergency Management (LINK) reported 370,000 customers without power. At 1:10 p.m. EDT Tuesday, poweroutage.us reported outages affecting 275,000 customers in Virginia, 785,000 in New Jersey, 110,000 in Maryland, 220,000 in Pennsylvania, 60,000 in Delaware, and 40,000 in New York. Power had been restored to 150,000 customers that had lost power in North Carolina, though.

White Stone, VA damage
Figure 4. Tornado damage in White Stone, Virginia, on August 4, 2020, after a twister spawned by Isaias injured two people. (Image credit: Jim Deaver)

Tornadoes strike the East Coast on the eastern flank of Isaias

Tornadoes often spin up within the “mini-supercells” that can develop along the rainbands of a landfalling hurricane or tropical storm. At least 18 preliminary tornado reports had already been received by NOAA’s Storm Prediction Center from Monday into Tuesday morning. Major damage was reported at a community of manufactured homes in Bertie County, North Carolina, where one person was reported killed, three were missing, and 20 injured (LINK). Another apparent twister led to two injuries and significant structural damage in White Stone, Virginia, and another caused damage Tuesday morning near Delaware’s capital city of Dover.

The winds funneling into Isaias from the east on Tuesday were shifting dramatically with height, leading to large low-level wind shear, and the powerful upper-level jet stream hauling Isaias northward led additional wind shear. The resulting spin added to the atmosphere generated a prolific regional outbreak of short-lived but damaging tornadoes. The areas most at risk were just ahead of Isaias and to the east of its track, pushing from New Jersey across the greater New York area and into Connecticut on Tuesday afternoon and evening. The NOAA Storm Prediction Center placed this region under an enhanced risk of severe weather.

Tornadoes from tropical cyclones are often on the weaker side, but they tend to develop and dissipate quickly, making it difficult to issue individual warnings – so residents should remain on guard, especially as the strongest thunderstorms approach. The same areas to the right of Isaias’s track will also be prone to damaging downburst gusts of 60 mph or more, as some of the upper-level wind could mix down within thunderstorms.

Next system to watch: 94L

A small low-pressure system, designated 94L by the National Hurricane Center, was located about 300 miles south-southwest of Bermuda at 8 a.m. EDT Tuesday, and was moving northwest at about 10 mph. Satellite images showed that the heavy thunderstorm activity associated with 94L had decreased significantly since Monday, and was very disorganized. The system was embedded in a dry atmosphere with a mid-level relative humidity of 50%, which was squelching development. On Wednesday, when 94L will be approximately midway between Bermuda and the Southeast U.S. coast, the system will be in an area of weak steering currents that will result in a slow and erratic motion. Late in the week, wind shear in that region is predicted to rise, and the atmosphere will remain dry, likely causing dissipation of 94L.
In an 8 a.m. EDT Tuesday Tropical Weather Outlook, the National Hurricane Center gave 94L two-day and five-day odds of formation of 30%. The system has only weak model support for development, and does not appear to be a threat to any land areas over the next five days.

The next name on the Atlantic list of storms is Josephine. The current record for earliest 10th Atlantic named storm formation is August 22, 2005, when Jose formed.

Bob Henson contributed to this post.

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Post Update on 8/3

Isaias update
Radar image of Tropical Storm Isaias at 11:36 a.m. EDT Monday, August 3, 2020. (Image credit: National Weather Service via Mark Nissenbaum/Florida State University)

Tropical Storm Isaias (pronounced ees-ah-EE-ahs) is poised to make landfall as a strong tropical storm or category 1 hurricane near the South Carolina/North Carolina border on Monday evening, making it the fifth U.S. landfalling named storm in this record-busy early portion of the 2020 hurricane season.

At 11 a.m. Monday, August 3, Isaias was located about 90 miles east of the coast of Georgia. The storm was moving north at 13 mph, with top winds of 70 mph and a central pressure that had risen to 998 mb.

Figure 1
Figure 1. Observed 24-hour precipitation amounts over Florida ending at 8 a.m. EDT Monday, August 3, 2020. Isaias dumped less than two inches of rain in the state (though some isolated 48-hour rainfall amounts just over two inches were reported). (Image credit: NOAA)

Isaias spares Florida

Isaias spared Florida major impacts as the storm brushed the state’s east coast with tropical storm-force winds and heavy rain showers over the weekend. Dry air and high wind shear teamed to keep Isaias just below hurricane strength during its march up the Florida coast, and Florida’s location on the dry side of the storm led to 24-hour rainfall amounts less than two inches everywhere in the state. Squalls moved into Miami-Dade County from the western edge of Isaias on Saturday, which led to localized 48-hour totals above 2″, including 2.31″ at the Miami National Weather Service office. As of 8 a.m. EDT Monday, August 3, about 3,000 customers in Florida were without power, according to poweroutage.us. On Jacksonville Beach, lifeguards rescued five people from rip currents and rough surf on Saturday, WJAX reported.

Figure 2
Figure 2. Visible GOES-17 satellite image of Hurricane Isaias at 11:10 a.m. EDT Monday, August 3, 2020. (Image credit: NOAA/RAMMB)

South Carolina radar and satellite images showed that Isaias had a somewhat ragged appearance on Monday afternoon, with a large area of intense thunderstorms along the northeast side of the center of circulation. Isaias was in a region dominated by westerly upper-level winds associated with a large-scale trough of low pressure. These winds were creating unfavorable conditions for intensification, with high wind shear of 20 – 25 knots. In addition, this shear was driving dry air from the west side of Isaias into its center, keeping heavy thunderstorms limited on its west side. The storm was attempting to build an eyewall (see Brian McNoldy’s long radar animations), but only about 50% of one was evident.

Sea surface temperatures (SSTs) were a warm 29 – 29.5 degrees Celsius (84 – 85°F), and Isaias was embedded in a moderately dry atmosphere with a mid-level relative humidity of 55 – 60%. Overall, these conditions point to little change to Isaias’s strength through landfall Monday evening near the South Carolina/North Carolina border, a point on which the intensity models and National Hurricane Center (NHC) forecast agree. Limited intensification just before landfall is being predicted by some of the intensity models, given a modest reduction in wind shear and the presence of the warm Gulf Stream waters, and Isaias will likely have top winds between 60 mph and 80 mph at landfall.

Figure 3
Figure 3. Predicted surface wind (colors) and pressure (black lines) at 03Z Tuesday (11 p.m. EDT Monday), from the 6Z Monday, August 3, 2020 run of the new HWRF model (which is scheduled to replace the old HWRF model in the next few weeks). The model predicted that Isaias would be making landfall near the South Carolina/North Carolina border as a category 1 hurricane with peak winds of 73 knots (84 mph, purple colors) and a central pressure of 982 mb. This is one of the strongest depictions of Isaias at landfall by the models. (Image credit: Tropical Tidbits)

Widespread power outages expected along U.S. East Coast

Tropical storm and hurricane warnings were up Monday for most of the U.S. East Coast from Georgia to Massachusetts, and tropical storm warnings will likely go up for the remainder of the northeastern U.S. coast, and also for portions of the Canadian Maritime provinces, on Monday evening. The main threat from the storm will be heavy rains in the mid-Atlantic and New England states, since the moist flow of air around the storm will interact with an unusually strong cold front to create areas of 4 – 6 inches of rain. The heavy rains, combined with the strong winds of the storm, will combine to cause widespread and long-lasting power outages, with the number of customers losing power along the storm’s track potentially exceeding 1 million. The corridor of strongest winds may be displaced just east of the heaviest rains, so locations such as far southeastern Virginia and the New Jersey coast could see very strong gusts, possibly extending into the New York City area.

Figure 4
Figure 4. Predicted three-day rainfall amounts from Isaias ending at 8 a.m. EDT Thursday, August 6, 2020. Isaias is expected to dump a widespread region of 4 – 6 inches of rain along its path, with isolated areas receiving in excess of six inches. (Image credit: NOAA/NHC)

While flash flooding is the main flood threat from Isaias, a damaging storm surge of 3 – 5 feet along portions of the Carolina coasts is also expected, and river flooding may be a problem in the Carolinas and also in the mid-Atlantic. River flooding will probably be less of an issue in the Northeast, which is generally in moderate drought, and where rainfall totals will be lower.

Figure 5
Figure 5. Drought conditions over the U.S. on July 28, 2020. (Image credit: U.S. Drought Monitor)

Next system to watch: 94L

NHC on Monday afternoon designated as 94L a tropical wave located about 300 miles north of Puerto Rico. Satellite images showed 94L moving northwest at about 15 mph, and having a modest amount of heavy thunderstorm activity that was slowly increasing in areal coverage.

Conditions were favorable for development, with wind shear a moderate 5 – 15 knots and sea surface temperatures a warm 28.5 degrees Celsius (83°F).

However, 94L was embedded in a dry atmosphere with a mid-level relative humidity of 50%, which will allow only slow development. On Tuesday, 94L will slow in forward speed, and beginning on Wednesday, when 94L will be approximately midway between Bermuda and the Southeast U.S. coast, the system will be in an area of weak steering currents that will result in a slow and erratic motion. Late in the week, wind shear in that region is predicted to rise, and the atmosphere will remain dry, potentially causing disruption and the possible dissipation of 94L.

Figure 6
Figure 6. Visible GOES-17 satellite image of 94L at 11:10 a.m. EDT Monday, August 3, 2020. (Image credit: NOAA/RAMMB)

In an 8 a.m. EDT Monday Tropical Weather Outlook, NHC gave 94L two-day and five-day odds of formation of 40% and 60%, respectively. The system has some weak model support for development, but does not appear to be a threat to any land areas over the next five days.

The next name on the Atlantic list of storms is Josephine. The current record for earliest 10th Atlantic named storm formation is August 22, 2005, when Jose formed.


Original Post on 8/2

Isaias on August 2
Radar image of Tropical Storm Isaias at 11:36 a.m. EDT Sunday, August 2, 2020. (Image credit: National Weather Service via Mark Nissenbaum/Florida State University)

Isaias (pronounced ees-ah-EE-ahs) was downgraded to tropical storm late Saturday afternoon, and is unlikely to regain hurricane strength as it performs a full tour of the U.S. East Coast on Sunday through Wednesday.

At 11 a.m. Sunday, August 2, Isaias had finished its pounding of the northwest Bahamas, and was located about 55 miles southeast of Fort Pierce, Florida. Isaias was moving north-northwest at 8 mph, nearly parallel to the Florida coast, and had top winds of 65 mph with a central pressure of 995 mb. An observing site at Settlement Point on the west end of Grand Bahama Island recorded sustained winds of 47 mph, gusting to 64 mph, at 10 a.m. EDT Sunday. Along the east coast of Florida, tropical-storm-force wind gusts were observed Sunday morning from Juno Beach northward to Port St. Lucie. A personal weather station on New Providence Island in the Bahamas received 4.53″ of rain from Isaias as of 11 a.m. EDT Sunday.

Figure 1
Figure 1. Visible GOES-17 satellite image of Hurricane Isaias at 15:20Z (11:20 a.m. EDT) Sunday, August 2, 2020. (Image credit: NOAA/RAMMB)

Florida radar showed that Isaias’s heavy rains were remaining mostly offshore on Sunday, with an intense area of rain focused near where the storm was struggling to build an eyewall. Satellite images showed that Isaias had a large area of intense thunderstorms along the east side of the center of circulation. Isaias was in a region dominated by westerly upper-level winds associated with a large-scale trough of low pressure. These winds were creating unfavorable conditions for intensification, with high wind shear of 20 – 25 knots. In addition, this shear was driving dry air from the west side of Isaias into its center, keeping heavy thunderstorms limited on its west side.

Sea surface temperatures (SSTs) were a warm 29 – 29.5 degrees Celsius (84 – 85°F), and Isaias was embedded in a moderately dry atmosphere with a mid-level relative humidity of 50 – 55%. With a portion of Isaias’s circulation over Florida, moisture supply to the storm was limited. Overall, these conditions point to little change to Isaias’s strength through Monday, a point on which the intensity models and National Hurricane Center (NHC) forecast agree.

Figure 2
Figure 2. Five-day rainfall amounts from Isaias ending at 8 a.m. EDT Friday, August 7, 2020. Isaias is expected to dump 4 – 6 inches of rain along portions of its path. (Image credit: NOAA/NHC)

Entire U.S. East Coast to get impacts from Isaias

Tropical storm warnings were up Sunday for most of the Southeast U.S. coast, and it is likely that nearly the entire U.S. East Coast will be under a tropical storm warning from Isaias at some time between Sunday and Tuesday. The main threat from the storm will be heavy rains in the mid-Atlantic and New England states, since the moist flow of air around the storm will interact with an approaching cold front to create widespread areas of 4 – 6 inches of rain.

Figure 3
Figure 3. Predicted surface wind (colors) and pressure (black lines) at 03Z Tuesday (11 p.m. EDT Monday), from the 6Z Sunday, August 2, 2020 run of the new HWRF model (which is scheduled to replace the old HWRF model in the next few weeks). The model predicted that Isaias would be making landfall near the South Carolina/North Carolina border as a strong tropical storm with peak winds of 62.5 knots (72 mph, dark red colors) and a central pressure of 986 mb. (Image credit: Tropical Tidbits)

Storm surge expert Dr. Hal Needham of u-surge.net wrote in an email that storm surge levels should generally peak at 1.5 to 3.5 feet along the coast from central Florida to extreme southern North Carolina. “The storm lacks the organization and tight wind field to generate a storm surge exceeding 4 feet, particularly since the eye will likely stay east of the Florida coastline,” Needham wrote. “Increasing forward speed inhibits the development of a substantial storm surge before Isaias makes a possible landfall in the Carolinas.”

The coast from northeast Florida to southern South Carolina is highly vulnerable to storm surge, as the offshore waters are very shallow and the concave shape of the coastline acts to funnel water onshore. Isaias will be the fourth named storm in the last five years to drive a notable storm surge to the coast in this region, joining Hurricane Dorian of 2019, Hurricane Irma of 2017, and Hurricane Matthew of 2016.

Figure 4
Figure 4. Sea surface temperatures (SSTs) off the U.S. East Coast on July 31, 2020. (Image credit: NOAA)

‘Severe’ to ‘extreme’ marine heat wave off the Mid-Atlantic and New England coasts will enhance Isaias’s rains

As reported by the Washington Post’s Capital Weather Gang on July 31, ocean temperatures along the mid-Atlantic and Northeast U.S. coasts are at record or near-record warmth, which will substantially increase the rainfall potential of Isaias and keep the storm stronger than it would otherwise be. SSTs at buoy 44066 (about 75 nm east of Long Beach, NJ) peaked at 27 degrees Celsius (81°F) on Saturday, and at the Nantucket Island station off the coast of Massachusetts, peaked at an astonishing 26.8 Celsius (80.2°F).

According to marineheatwaves.org, the waters along the coast from New Jersey to Maine are experiencing a “severe” to “extreme” marine heatwave (MHW). An MHW is defined as when the temperature in a given location is in the top 10% of temperatures ever recorded during that time of year for at least five straight days. A “severe” MHW is uncommon, and can be devastating to marine ecosystems if it persists for more than a month. An “extreme” MHW is very rare, and can wipe out an entire coastal ecosystem if it persists for more than three months. Fortunately, Isaias’s strong winds are going to churn the waters of these marine heat wave areas, reducing their intensity by mixing up cooler waters.

Figure 5
Figure 5. Visible GOES-17 satellite image of 94L at 10 a.m. EDT Sunday, August 2, 2020. (Image credit: NOAA/RAMMB)

Next system to watch for development: 94L

A tropical wave located about 300 miles east of the Leeward Islands on Sunday morning, August 2, was designated 94L by NHC on Saturday evening. Satellite images on Sunday afternoon showed 94L moving northwest at about 15 mph, and having a modest amount of heavy thunderstorm activity that was slowly growing more organized.

Conditions were favorable for development, with wind shear a low 5 – 10 knots and SSTs a warm 28.5 degrees Celsius (83°F).

However, 94L was embedded in a dry atmosphere with a mid-level relative humidity of 50%, which will slow development. Continued development of 94L is likely as it passes northeast of the Leeward Islands on Sunday and Monday. In an 8 a.m. EDT Sunday Tropical Weather Outlook, NHC gave 94L two-day and five-day odds of formation of 30% and 60%, respectively. Although the system has some model support for development, it does not appear to be a threat to any land areas over the next five days.

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The next name on the Atlantic list of storms is Josephine. The current record for earliest 10th Atlantic named storm formation is August 22, 2005, when Jose formed.

Tropical Depression Ten, meanwhile, dissipated north of the Cabo Verde Islands on Saturday evening.

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Topics: Weather Extremes
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Gary Townley
Gary Townley
1 month ago

I forgot to add that the video was captured by a meteorologist in Westport Connecticut.

Gary Townley
Gary Townley
1 month ago

I thought you might be interested Dr. Masters. A waterspout moved inland off of Longisland Sound on to land in Westport, CT to become a tornado. It was the first such occurrence ever recorded in Connecticut of a waterspout turning into a tornado. It was rated as a EF1 by the National Weather Service in New York. A video of it can be found on YouTube https://youtu.be/SmP7Hx4lrbA

FLORIDAIKE
FLORIDAIKE
1 month ago

Checking in first time.

Amature Met
Amature Met
1 month ago
Reply to  FLORIDAIKE

Yes, you are here, Not much happening.

Skyepony
1 month ago

11L looking gamely..

0812163011L.gif
Skyepony
1 month ago
Reply to  Skyepony

Click pic for animation..

Amature Met
Amature Met
1 month ago
Reply to  Skyepony

Looks to still be attached to the ITCV. Shear about to drop to 0-5 knots. Got cloced coc warm water low to no shear comming, yea, very gamey,

A total ACE of 10-15 before its done?

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