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. My latest birdseye view chart and post of the Atlantic tropics up at this link. After a weekend of updating on the cellphone, back to the normal fully annotated charts marking the situation with each storm. Discussion of the increasing threat from Delta to the Cayman Islands, western Cuba, and US Gulf coast near Louisiana and Mississippi included. This is not good news at all as Gamma is losing the battle with the increasingly formidable Tropical Storm Delta.

  2. https://www.nejm.org/doi/full/10.1056/NEJMp2023830?query=featured_home

    Pay particular attention to Paragraph 10, read it twice and let the math numbers and the science sink in deeply. Think about all those walking around our own top levels of government right now after a superspreading storm. And those great and oh so reliable results, spreading the virus far and wide possibly still.

    Watching the weather closely, but feeling the effects of the man (very poorly), managed viral storm more at this particular time.

  3. We will have 2 prs of tiny dancers, a pr in each basin. Marie and 95E (appears to be fully closing it’s circulation center), in EPAC, and GAMMA and Delta in the WATL GOM/CS. Certainly means we should start the day off with an Elton John song after the world’s Rainbow #Proud Boys took back their hashtag from the Hateful TrumptyDUMP Proudy Bois and decorated it all up with sequined rainbows….lmao when I saw that on the news. (Oh boy, the AR-15’s and bear spray will be a blazin today!)

    1. I did follow that up with Stevie Nicks – Edge of Seventeen as it sounds much more like an impending storm moving in….

      1. Followed by 1 reflecting the very hopefully cool (and eventually Delta weakening), Gulf Coast sea temps…Prince – Purple Rain. And the new Trump Scampaign song for our sadly hospitalized Pres….Gnarls Barkley – Crazy long version.

        Yes, it is music monday folks….Because nothing, and I mean absolutely nothing, but music makes sense these days…

        It didn’t have to be this way! (Received news last night that another good friend was taken by covid-19, makes 1 Aunt, 15 pretty close friends….For some, life simply does not go on.

        It Ain’t No HOAX…Mask up and distance folks! Please……

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