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Tropical Storm Nana Forecast Discussion Number 4
2020-09-02 04:37:15| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Tue Sep 01 2020 000 WTNT41 KNHC 020237 TCDAT1 Tropical Storm Nana Discussion Number 4 NWS National Hurricane Center Miami FL AL162020 1100 PM EDT Tue Sep 01 2020 Deep convection redeveloped over the center of Nana during the late afternoon and recent microwave imagery has revealed a small, well-defined low-level eye-like feature, and convective banding around the southwestern portion of the circulation. An Air Force Reserve hurricane hunter aircraft that has provided a couple of center fixes within the past hour or two has measured a peak 850-mb flight-level wind of 62 kt, and believable SFMR winds of around 50 kt, which supports an initial intensity of 50 kt. Data from aircraft indicated that the minimum pressure is around 999 mb. Nana is moving westward or 275/16 kt. A strong deep-layer ridge to the north of the tropical cyclone should steer it westward over the next day or so. After that time, the ridge is forecast to build west-southwestward and the dynamical models indicate that this will cause Nana to turn west-southwestward by Thursday. On this track, Nana is expected to approach the coast of Belize late Wednesday night or early Thursday, and move inland over Belize and Guatemala later that day. The track guidance is in good agreement on this scenario but has trended slightly southward, which seems reasonable given that Nana is vertically deep and is more likely to feel the deep-layered east-northeasterly flow. The new NHC track forecast is close to the FSU Superensemble and the HFIP corrected consensus model. The tropical storm is currently within an environment of light to moderate northeasterly shear. This shear does not seem to be strong enough to prevent strengthening during the next 12-24 hours, and the NHC intensity forecast shows a slightly faster rate of intensification during that time. This is in agreement with the latest SHIPS model output and the HCCA and HWRF models, and calls for Nana to become a hurricane within 24 hours. The shear is forecast to become more northerly just before landfall, and this is likely to slow the intensification process. Rapid weakening is expected after landfall, and the low-level circulation is expected to dissipate over Guatemala or southeastern Mexico by day 3. KEY MESSAGES: 1. Tropical Storm Nana is forecast to be a hurricane as it approaches the coast, and interests in Honduras, Guatemala, Belize, and Yucatan should closely monitor the progress of this storm. Strong winds, dangerous storm surge and very heavy rainfall causing flash flooding are becoming more likely from Nana. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 17.0N 80.9W 50 KT 60 MPH 12H 02/1200Z 17.1N 83.5W 60 KT 70 MPH 24H 03/0000Z 17.0N 86.3W 65 KT 75 MPH 36H 03/1200Z 16.8N 88.6W 65 KT 75 MPH...INLAND 48H 04/0000Z 16.5N 90.7W 35 KT 40 MPH...INLAND 60H 04/1200Z 16.2N 93.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 05/0000Z...DISSIPATED $$ Forecaster Brown
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