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| #1019898 (Received by flhurricane at: 5:03 PM 04.Oct.2020) TCDAT5 Tropical Storm Gamma Discussion Number 10 NWS National Hurricane Center Miami FL AL252020 400 PM CDT Sun Oct 04 2020 The last aircraft reconnaissance fix, recorded a couple of hours ago, indicated that Gamma`s center had wobbled a little to the right of the previous 6-hour motion and is located near the southeastern edge of the convective canopy. Flight-level winds adjusted to the surface, SFMR wind data, and a blend of Dvorak satellite intensity estimates from TAFB and SAB still support an initial intensity of 50 kt for this advisory. The UW-CIMSS shear analysis reveals stiff 20-25 kt southerly shear impinging on the south portion of the cyclone. Subsequently, the large-scale models and the ECMWF/GFS statistical-dynamical intensity guidance show the shear magnitude increasing during the next 24 hours. This inhibiting upper wind pattern should induce weakening soon. Although the shear is predicted to decrease somewhat around mid-period, Gamma should exhibit little change in strength through the remaining period which is in best agreement with all of the skilled intensity guidance. As mentioned in previous advisories, it cannot be stressed enough the relatively high level of uncertainty in this intensity forecast, and that it`s primarily dependent on whether or not the cyclone moves back over the Yucatan Peninsula. Gamma should continue to move little, or meander over the southern Gulf of Mexico, near the northern coast of the Yucatan Peninsula through most of tomorrow. By Monday night, the global models are in good agreement with the western extent of a subtropical ridge reestablishing temporarily over the central Gulf of Mexico. This change in the synoptic steering pattern should cause the cyclone to turn and move west-southwestward through the 72 hour forecast period. After a brief reduction in forward speed late Wednesday, while Potential-Tropical Cyclone Twenty-Six moves into the central Gulf of Mexico, a turn toward the northwest is expected on Thursday as the ridge, once again, builds back over the central Gulf in response to PTC Twenty-Six approaching the northern Gulf coast. The official track forecast is adjusted to the left of the previous one through the 60 hour period to agree more with the HCCA consensus, and shifted to the right through day 5. KEY MESSAGES: 1. Gamma is expected to produce heavy rainfall for several days over portions of southeastern Mexico, the Yucatan Peninsula, Central America, and far western Cuba. This rainfall could result in life-threatening flash flooding and mudslides, particularly in the mountainous regions of southeastern Mexico and Central America. 2. Even though Gamma is just offshore, tropical storm conditions will continue across portions of the northern coast of the Yucatan Peninsula today. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 22.4N 87.8W 50 KT 60 MPH 12H 05/0600Z 22.3N 88.1W 45 KT 50 MPH 24H 05/1800Z 22.1N 88.6W 40 KT 45 MPH 36H 06/0600Z 21.7N 89.4W 40 KT 45 MPH 48H 06/1800Z 21.3N 90.4W 40 KT 45 MPH 60H 07/0600Z 20.8N 91.1W 40 KT 45 MPH 72H 07/1800Z 20.1N 91.4W 40 KT 45 MPH 96H 08/1800Z 21.0N 92.1W 40 KT 45 MPH 120H 09/1800Z 22.2N 92.7W 40 KT 45 MPH $$ Forecaster Roberts |