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| #938420 (Received by flhurricane at: 10:57 PM 03.Sep.2018) TCDAT2 Tropical Storm Gordon Discussion Number 7 NWS National Hurricane Center Miami FL AL072018 1100 PM EDT Mon Sep 03 2018 WSR-88D radar data from Tampa shows that the small inner core of Gordon has lost some organization during the past few hours, and GOES-16 satellite imagery and recent aircraft fixes indicate that the low-level center is located near the southwestern edge of the main convective mass. This suggests that there may be some light to moderate westerly shear affecting the cyclone. The Air Force Reserve reconnaissance aircraft recently measured peak 850-mb flight-level winds of 57 kt, and SFMR winds of 50-55 kt. A blend of these data yields an initial wind speed estimate of 50 kt. A UW/CIMSS shear analysis and the SHIPS model indicates that there is about 10-15 kt of westerly shear over the system. The SHIPS guidance shows a slight relaxation of the shear during the next 12-18 hours while the system moves over the warm waters of the Gulf of Mexico, which should allow for some strengthening. However, Gordon is a small tropical cyclone and subtle changes in shear (both up and down) can result in fairly quick intensity changes for systems like this. The NHC intensity forecast assumes that shear will not be prohibitive and that Gordon will become a hurricane before reaching the northern Gulf coast. The NHC intensity forecast is close to the SHIPS guidance through 24 hours, then follows the HFIP corrected consensus after landfall which shows Gordon weakening rapidly over land. Gordon is moving west-northwestward at about 15 kt. The tropical storm is expected to maintain a west-northwestward to northwestward heading during the next few days while it moves around the southwestern portion of a large deep-layer ridge centered over the Mid-Atlantic states. After that time, the cyclone should decelerate as it moves around the western periphery of the ridge. The track guidance continues to be tightly clustered through 72 h, and no significant changes were required to the previous NHC track forecast. Key Messages: 1. Gordon is expected to bring life-threatening storm surge and hurricane conditions to portions of the central Gulf Coast where a Storm Surge Warning and Hurricane Warning are in effect. Residents in these areas should listen to advice from their local officials. All preparations to protect life and property should be rushed to completion, as tropical storm conditions are expected to arrive in the warning areas Tuesday afternoon. 2. Heavy rainfall from Gordon will affect southern Alabama, southern Mississippi and Louisiana, where totals could reach as high as 8 inches. This rainfall could cause flash flooding. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 26.9N 84.3W 50 KT 60 MPH 12H 04/1200Z 28.3N 86.3W 55 KT 65 MPH 24H 05/0000Z 30.0N 88.6W 65 KT 75 MPH 36H 05/1200Z 31.6N 90.3W 40 KT 45 MPH...INLAND 48H 06/0000Z 32.9N 91.6W 25 KT 30 MPH...INLAND 72H 07/0000Z 34.6N 93.9W 20 KT 25 MPH...INLAND 96H 08/0000Z 36.5N 94.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 09/0000Z 39.5N 93.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown |