Gamma satellite image
GeoColor satellite image of Tropical Storm Gamma near Mexico's Yucatan Peninsula (left) and Invest 92L southeast of Jamaica (right) at 11:30 a.m. EDT Sunday, October 4, 2020. (Image credit: RAMMB/CIRA/Colorado State University)

A tropical wave located in the central Caribbean southeast of Jamaica on Sunday afternoon, designated 92L by the National Hurricane Center, is likely to develop into Tropical Storm Delta by Tuesday, with the potential to strengthen into a hurricane in the Gulf of Mexico late this week.

Early Sunday afternoon, 92L was headed west-northwest at about 10 mph, and was spreading heavy rain showers over Jamaica and Haiti. Satellite images showed 92L growing more organized and with modest but steadily increasing thunderstorm activity. Its surface circulation was attempting to develop about 100 miles southeast of Jamaica. But under a moderate 15-20 knots of wind shear, 92L was experiencing slowing development.

Figure 1. Track forecasts out to eight days for Invest 92L from the 6Z (2 a.m. EDT) Sunday, October 4, run of the new version of the GFS ensemble model (GEFS). The black line is the mean of the 31 ensemble members; individual ensemble member forecasts are the thin lines, color-coded by the central pressure. Seven of the 31 members called for 92L to hit the U.S. as a strong tropical storm or as a hurricane (orange and red colors). (Image credit: Tropical Tidbits)

Forecast for 92L

When 92L reaches the western Caribbean on Monday, the shear is expected to drop to just 5-10 knots, ocean temperatures beneath its path will be 30 degrees Celsius (86°F), and 92L will be in a moist environment – conditions that favor development. The 0Z Sunday runs of the top three models for predicting tropical cyclone genesis were giving only modest support for development, but the 12Z Sunday run of the GFS model predicted that 92L would be a hurricane in the Gulf of Mexico by Thursday, as were several of the 31 members of the 6Z Sunday run of the GFS ensemble model (Figure 1). The majority of the top intensity models – which should not be trusted until a disturbance actually develops into a tropical depression – also were predicting that 92L would be a hurricane by Thursday. The track forecast for 92L may be complicated by the presence of Tropical Storm Gamma to the southwest, as the two could be close enough together to cause them to rotate counter-clockwise around each other.

The warmest waters with high heat content along 92L’s path are in the western Caribbean and southern Gulf of Mexico. Once 92L penetrates into the central Gulf, it will encounter a cool eddy with limited heat content. In the northern Gulf of Mexico, waters are comparatively cool, about 26 degrees Celsius (79°F). This cooler temperature is partially the result of the mixing caused by the passage of Hurricane Sally in mid-September. As a result, it will be difficult for 92L to be strengthening at the time of a potential landfall along the northern U.S. Gulf Coast.

In an 8 a.m. EDT Sunday Tropical Weather Outlook, the National Hurricane Center gave 92L two-day and five-day odds of development of 70% and 80%, respectively. The next name on the Atlantic list of storms is Delta. The first hurricane hunter mission into 92L is scheduled for Monday afternoon.

Figure 2. Sea surface temperatures (SSTs) in the Gulf of Mexico on October 2 were quite cool near the central U.S. Gulf Coast, about 26 degrees Celsius (79°F). (Image credit: NOAA)

Gamma made landfall in Mexico’s Yucatan Peninsula

Tropical Storm Gamma made landfall in Mexico’s Yucatan Peninsula early Saturday afternoon with top winds of 70 mph, just below hurricane strength, bringing heavy rains to portions of the Yucatan Peninsula, western Cuba, and Central America. According to Conagua, 9.63 inches of rain fell on Cozumel in the 24 hours ending at 8 a.m. EDT Saturday. At 11 a.m. EDT Sunday, Gamma was over the southern Gulf of Mexico, just off the coast of the Yucatan Peninsula, moving north at just 2 mph.

Forecast for Gamma

Conditions for development of Gamma will be unfavorable through Thursday, with high wind shear of 15 – 30 knots and a dry atmosphere (a mid-level relative humidity of 40 – 60%). The top intensity models and the official NHC forecast all predict slow weakening of Gamma through Thursday.

Also see: At least three named Atlantic storms likely during October

Gamma is caught in an area of weak steering currents, and a slow west to west-southwest motion at less than 5 mph is expected throughout most of the week, as a weak ridge of high pressure builds to the north of the storm. Gamma’s slow motion will result in heavy rains across much of Mexico’s Yucatan Peninsula and portions of Central America.

NHC on Sunday morning gave two other areas of interest in the central Atlantic low odds of development, with neither of these systems a threat to any land areas.

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Posted on October 4, 2020 (1:55pm EDT).

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...

50 replies on “Tropical Storm Delta likely to form by Tuesday”

  1. Japan Meteorological Agency
    Tropical Cyclone Advisory #9 – 21:00 PM JST October 5 2020
    TROPICAL STORM CHAN-HOM (T2014)
    =================================================
    Sea South of Japan

    At 12:00 PM UTC, Tropical Storm Chan-hom (998 hPa) located at 22.4N 139.2E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as almost stationary.

    Gale Force Winds
    ==================
    210 nm from the center in southeastern quadrant
    90 nm from the center in northwestern quadrant

    Dvorak Intensity: T2.0

    Forecast and Intensity
    =========================
    24 HRS: 24.0N 137.7E – 50 knots (CAT 2/Severe Tropical Storm) Sea South of Japan
    48 HRS: 25.7N 133.7E – 70 knots (CAT 3/Strong Typhoon) 250 km east of Minami-daito Island (Okinawa Prefecture)
    72 HRS: 27.9N 131.5E – 75 knots (CAT 3/Strong Typhoon) south of Kyushu region of Japan (Kagoshima Prefecture)

  2. BULLETIN
    Tropical Storm Delta Intermediate Advisory Number 3A
    NWS National Hurricane Center Miami FL AL262020
    800 AM EDT Mon Oct 05 2020

    …TROPICAL DEPRESSION STRENGTHENS INTO A TROPICAL STORM…
    …ADDITIONAL STRENGTHENING LIKELY OVER THE NEXT FEW DAYS…

    SUMMARY OF 800 AM EDT…1200 UTC…INFORMATION
    ———————————————-
    LOCATION…16.4N 78.4W
    ABOUT 130 MI…210 KM S OF NEGRIL JAMAICA
    ABOUT 270 MI…440 KM SE OF GRAND CAYMAN
    MAXIMUM SUSTAINED WINDS…40 MPH…65 KM/H
    PRESENT MOVEMENT…WNW OR 290 DEGREES AT 9 MPH…15 KM/H
    MINIMUM CENTRAL PRESSURE…1004 MB…29.65 INCHES

  3. Michael Ventrice showed an animation yesterday of Gamma decoupling. Looks similar to what we see this morning. His animation showed this happing sooner though. It was hard to see LLC from the NHC website. I wish they would let us have option to control the time period & speed of the satellite loops.

  4. Japan Meteorological Agency
    Tropical Cyclone Advisory #7 – 15:00 PM JST October 5 2020
    TROPICAL STORM CHAN-HOM (T2014)
    ===============================================
    Sea South of Japan

    At 6:00 AM UTC, Tropical Storm Chan-hom (996 hPa) located at 22.3N 139.2E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as almost stationary.

    Gale Force Winds
    ==================
    180 nm from the center in southern quadrant
    90 nm from the center in northern quadrant

    Dvorak Intensity: T2.0-

    Forecast and Intensity
    =========================
    24 HRS: 24.2N 138.3E – 50 knots (CAT 2/Severe Tropical Storm) Sea South of Japan
    48 HRS: 25.8N 134.9E – 70 knots (CAT 3/Strong Typhoon) 370 km east of Minami-daito Island (Okinawa Prefecture)
    72 HRS: 27.8N 132.3E – 75 knots (CAT 3/Strong Typhoon) Sea South of Japan

  5. The NHC forecast predicted Gamma to go SW as of 7:00 PM advisory. It looks like Gamma went much further North & East. I am looking for LLC. Did COC relocate under deep convection to the north? These sloppy systems that are sheared make it hard to locate COC and then there is always possibility of relocation under deep convection.

    1. I saw one model take Gamma north and weaken some and Join in with 26 and go into New Orleans area together..i guess in this crazy season anything is possible huh

  6. Japan Meteorological Agency
    Tropical Cyclone Advisory #5 – 9:00 AM JST October 5 2020
    TROPICAL STORM CHAN-HOM (T2014)
    ======================================================
    Sea South of Japan

    At 0:00 AM UTC, Tropical Storm Chan-hom (998 hPa) located at 22.2N 139.0E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The cyclone is reported as moving west slowly.

    Gale Force Winds
    ==================
    150 nm from the center in southern quadrant
    75 nm from the center in northern quadrant

    Dvorak Intensity: T2.0-

    Forecast and Intensity
    =========================
    24 HRS: 23.5N 138.7E – 45 knots (CAT 1/Tropical Storm) Sea South of Japan
    48 HRS: 25.4N 136.1E – 60 knots (CAT 2/Severe Tropical Storm) 490 km east of Minami-daito Island (Okinawa Prefecture)
    72 HRS: 27.0N 132.7E – 70 knots (CAT 3/Strong Typhoon) Sea South of Japan

  7. Nothing simpler than tropical soup. But bowls of clouds are alot better. Part of this complete breakfast. So wash your hands and have 2 weeks worth of vacation

  8. Good afternoon folks, my latest birdseye view post which includes a discussion on PTC 26 and TS Gamma is up at this link. I am not quiet sure yet about PTC 26 becoming TS Delta, especially if it loses the battle with TS Gamma (two tropical systems near each other tend to fight and one will win, or alternatively they both stay on the weaker side if one does not dominate over the other). But if it goes on to survive its battle with Gamma, then yes it will become a problem for the US Gulf coast.

  9. Hate to say this but I am betting Delta has Pensacola/Mobile written all over it again. That low is going to be east of it soon.

  10. India Meteorological Department
    Tropical Disturbance Summary
    17:30 PM IST October 4 2020
    =============================================

    A fresh low pressure area is very likely to form over northern Andaman sea and adjoining east central Bay of Bengal around October 9th. It is very likely to move northwestward towards northern Andhra Pradesh and Odisha coasts with gradual intensification into a depression during the subsequent 2-3 days.

  11. Thanks for the Sunday update, Dr. Masters! Going to be an interesting week to say the least….

  12. Japan Meteorological Agency
    Tropical Cyclone Advisory #3 – 3:00 AM JST October 5 2020
    TROPICAL DEPRESSION 16
    ===============================================
    Sea South of Japan

    At 18:00 PM UTC, Tropical Depression (1000 hPa) located at 22.2N 139.3E has 10 minute sustained winds of 30 knots. The depression is reported as almost stationary.

    Dvorak Intensity: T1.5

    Forecast and Intensity
    =========================
    24 HRS: 24.2N 138.7E – 40 knots (CAT 1/Tropical Storm) Sea South of Japan
    48 HRS: 25.0N 137.0E – 60 knots (CAT 2/Severe Tropical Storm) Sea South of Japan
    72 HRS: 26.4N 133.0E – 70 knots (CAT 3/Strong Typhoon) Sea South of Japan

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