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Tropical Storm Gamma Discussion Number  12
NWS National Hurricane Center Miami FL       AL252020
400 AM CDT Mon Oct 05 2020
 
Gamma is a strongly sheared tropical storm that has been meandering 
just north of the northern coast of the Yucatan Peninsula of Mexico. 
Strong convective cloud tops colder than -80 deg C are located more 
than 60 nmi north and northeast of the well-defined and fully 
exposed low-level circulation center. An Air Force Reserve 
reconnaissance aircraft investigating the cyclone found maximum 
850-mb flight-level winds of only 44 kt along with peak SFMR surface 
winds of 47 kt. In addition, a 0329Z ASCAT-A pass revealed peak 
surface winds of 41 kt. Allowing for undersampling by the 
scatterometer instrument and blending it with the SFMR winds 
supports lowering the initial intensity to 45 kt. The central 
pressure of 999 mb is based on a center dropsonde reports of 1000 mb 
and 10-12 kt winds.

The initial motion estimate is an uncertain 240/02 kt. Gamma's 
future track remains highly uncertain after day 2. For the next 48 
hours or so, the cyclone is forecast to move slowly southwestward to 
west-southwestward and weaken due to strong southerly vertical wind 
shear. Thereafter, TD-26 to the east is forecast to strengthen into 
a hurricane, accompanied by a corresponding increase in the size of 
that cyclone's circulation, which is expected to result in some 
binary interaction between the two tropical cyclones. Due to Gamma's 
expected smaller size on days 3 and 4, the cyclone is forecast to be 
pulled eastward and then northward, making landfall on and then 
moving over the northwestern Yucatan Peninsula. By day 5, Gamma is 
expected to degenerate into a remnant low and then be absorbed by 
the larger circulation of the expected central Gulf of Mexico 
hurricane that is currently TD-26. The new NHC track forecast is 
similar to but a little slower than the previous advisory track, and 
lies close to the southern edge of the guidance envelope.

Strong southerly wind shear, combined with drier and more stable air 
just to the west of Gamma, is expected to weaken the cyclone further 
over the next few days. If land interaction occurs sooner than 
expected, then the cyclone could weaken and dissipate sooner than 
currently forecast. For now, the intensity forecast maintains 
continuity with the previous advisory and shows dissipation by 120 
hours as Gamma interacts with what is expected to be a significant 
hurricane over the central Gulf of Mexico by 96 hours, which could 
end up absorbing the smaller Gamma tropical cyclone.
 
Due to the uncertainty in the forecast at this time, future 
advisories may feature larger-than-normal changes to the track or 
intensity forecast. It is also worth noting that several dynamical 
model trackers appear to lose Gamma and jump to tracking Tropical 
Depression Twenty-Six when it reaches the Gulf of Mexico, resulting 
in unrealistic depictions of the model intensity and track 
forecasts.
 
KEY MESSAGES:
 
1. Gamma is expected to produce heavy rainfall through midweek over 
portions of southeast Mexico, including the Mexican states of 
Yucatan, Campeche, and Tabasco. This rainfall could result in 
significant flash flooding.
 
2. Even though Gamma is just offshore, tropical storm conditions
are likely along portions of the northern coast of the Yucatan
Peninsula later today.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/0900Z 22.7N  87.5W   45 KT  50 MPH
 12H  05/1800Z 22.5N  88.0W   40 KT  45 MPH
 24H  06/0600Z 22.1N  88.9W   40 KT  45 MPH
 36H  06/1800Z 21.4N  89.8W   35 KT  40 MPH
 48H  07/0600Z 20.8N  90.4W   35 KT  40 MPH
 60H  07/1800Z 20.3N  90.5W   30 KT  35 MPH...INLAND YUCATAN
 72H  08/0600Z 20.7N  90.1W   30 KT  35 MPH...INLAND YUCATAN
 96H  09/0600Z 22.5N  90.0W   30 KT  35 MPH...OVER WATER
120H  10/0600Z...DISSIPATED
 
$$
Forecaster Stewart
 
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