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Tropical Storm Vicente Forecast Discussion Number 4
2018-10-20 10:37:06| National Hurricane Center (East Pacific)
Issued at 400 AM CDT Sat Oct 20 2018 000 WTPZ43 KNHC 200836 TCDEP3 Tropical Storm Vicente Discussion Number 4 NWS National Hurricane Center Miami FL EP232018 400 AM CDT Sat Oct 20 2018 Radar data from Guatemala indicate that Vicente remains a very small but well-defined tropical cyclone, which has occasionally exhibited an eye-like feature. However, convection has waned during the past few hours, so it is difficult to accurately ascertain the intensity of such a tiny storm since small systems like this can spin up and spin down very quickly owing to minor convective fluctuations. For now, it is assumed that Vicente is still a tropical storm based on satellite intensity estimates of T2.5/35 kt from TAFB and SAB, and 41 kt from UW-CIMSS SATCON; the most recent ADT value, however, was T2.2/32 kt. The initial motion estimate is 290/06 kt. Over the last 18 hours, it appears that Vicente's track has been doing some coastal hugging. That being said, the tropical storm is expected to turn more westward during the next 12 h and emerge over the open Gulf of Tehuantepec where a modest gap wind event is forecast to turn the cyclone southwestward by this evening. The latest 00Z model guidance is surprisingly in very good agreement on the development of this unusual track scenario. By 36-48 hours, a gradual turn toward the west is expected, followed by a motion toward the northwest on days 3-5 as the small cyclone rounds the southwestern periphery of a deep-layer ridge located over the Gulf of Mexico and central Mexico. Assuming Vicente survives the next 96 hours, on day 5 the tropical cyclone is expected to come under the influence of the new and much larger Tropical Depression 24-E -- currently located about 700 nmi to the west -- and possibly become absorbed or forced inland over southwestern Mexico by that system. The new NHC forecast was nudged a little to the west at most forecast times, closer to the HCCA and FSSE corrected consensus models. Vertical shear is forecast to be less than 10 kt and the mid-level moisture is expected to be high with humidity values of more than 75 percent for the next 36 hours. This should allow for some gradual strengthening to occur during that time despite Vicente's proximity to land. By 48 hours and beyond, however, northerly shear is expected to increase across the small cyclone, which should act to cap the intensification process and induce some gradual weakening by 96h. On day 5, the shear is forecast to exceed 20 kt, due in large part to the expected strong outflow from a strengthening TD-24E, resulting in significant weakening or even dissipation of Vicente. The official intensity forecast is similar to but slightly below the previous forecast, and lies close to an average of the HCCA, FSSE, and IVCN consensus models. Vicente should begin to slowly pull away from the coast overnight and on Saturday, however, heavy rainfall, with possible life-threatening flash flooding, is expected over portions southeastern Mexico during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 14.0N 93.1W 35 KT 40 MPH 12H 20/1800Z 14.1N 93.9W 35 KT 40 MPH 24H 21/0600Z 13.5N 95.3W 40 KT 45 MPH 36H 21/1800Z 12.9N 97.1W 40 KT 45 MPH 48H 22/0600Z 13.1N 98.7W 45 KT 50 MPH 72H 23/0600Z 15.2N 101.9W 50 KT 60 MPH 96H 24/0600Z 18.3N 104.9W 50 KT 60 MPH 120H 25/0600Z 21.8N 108.3W 35 KT 40 MPH $$ Forecaster Stewart
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