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| #1022659 (Received by flhurricane at: 4:57 AM 26.Oct.2020) TCDAT3 Tropical Storm Zeta Discussion Number 7 NWS National Hurricane Center Miami FL AL282020 500 AM EDT Mon Oct 26 2020 Zeta`s satellite presentation has continued to improve overnight. The cold convective cloud shield has expanded northwestward over the center and there has been a continued increase in banding over the southern and southeastern portions of the circulation. With the expansion of the convection over the center, it appears that a CDO feature is trying to form. A NOAA P-3 reconnaissance aircraft that has been investigating Zeta overnight has reported that the pressure has fallen to 990 mb. The aircraft has found peak 850-mb flight-level winds of 69 kt and believable SFMR winds of around 60 kt, with some higher flagged values. These data support increasing the initial intensity to 60 kt for this advisory. Recent aircraft fixes indicate that Zeta has begun its expected northwestward motion at about 315 degrees at 8 kt. The storm should begin to move at an even faster pace toward the northwest as a mid-level ridge builds over the western Atlantic and Florida during the next 24 to 36 hours. This ridge will steer Zeta across the northern portion of the Yucatan peninsula tonight, and over the south-central Gulf of Mexico on Tuesday. A vigorous mid- to upper-level trough currently over the western United States is forecast to begin ejecting out of the southwestern U.S. by mid-week, which will erode the western portion of the aforementioned ridge. This should cause Zeta to accelerate northward and approach the northern Gulf of Mexico on Wednesday. The 0000 UTC global models, which incorporated dropwindsonde data from the earlier NOAA G-IV synoptic surveillance mission, have come into somewhat better agreement this cycle. While there is still some spread on exactly when the northward turn takes place and how quickly Zeta accelerates north-northeastward over the Gulf of Mexico, the cross-track spread at 60 h is about half of what it was before, resulting in an increase in track-forecast confidence. The latest NHC track is in best agreement with the GFS ensemble mean and the GFEX consensus aid. This is a little right of the TVCA and HCCA multi-model consensus, but quite close to the previous NHC track forecast. With the recent improvement in the outflow over Zeta, it appears that the shear that had prevented strengthening has abated. The shear ahead of the storm is expected to remain low while the cyclone traverses the deep, warm water of the northwestern Caribbean Sea. As a result, Zeta is forecast to become a hurricane this morning, and continued strengthening is likely until Zeta moves over the Yucatan peninsula this evening. The landfall intensity is likely to be a little stronger than shown below since Zeta will be inland over the Yucatan peninsula by the 24-hour forecast point. Environmental conditions over the southern Gulf of Mexico are forecast to be conducive for some re-strengthening as Zeta moves over the south-central Gulf on Tuesday. Increasing shear and the cooler shelf waters of the northern Gulf are likely to result in some reduction in intensity before Zeta reaches the northern Gulf coast. KEY MESSAGES: 1. Hurricane conditions and storm surge are expected in portions of the northern Yucatan Peninsula of Mexico tonight and early Tuesday. Tropical storm conditions could occur over extreme western Cuba beginning later today. 2. Through Tuesday, heavy rainfall is expected from Zeta across the Yucatan Peninsula of Mexico, the Cayman Islands, and central to western Cuba. This rainfall may lead to flash flooding in urban areas. 3. Zeta is forecast to be at or near hurricane strength when it approaches the northern Gulf Coast on Wednesday, and there is an increasing risk of storm surge, rainfall, and wind impacts from Louisiana to the Florida Panhandle. Residents in these areas should monitor the progress of Zeta and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 18.7N 84.3W 60 KT 70 MPH 12H 26/1800Z 19.5N 85.5W 75 KT 85 MPH 24H 27/0600Z 20.8N 87.5W 75 KT 85 MPH...INLAND 36H 27/1800Z 22.5N 89.6W 65 KT 75 MPH...OVER WATER 48H 28/0600Z 24.7N 91.1W 70 KT 80 MPH 60H 28/1800Z 27.7N 90.8W 65 KT 75 MPH 72H 29/0600Z 31.8N 88.2W 45 KT 50 MPH...INLAND 96H 30/0600Z 39.0N 75.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 31/0600Z...DISSIPATED $$ Forecaster Brown |
