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Tropical Storm MARTY Forecast Discussion Number 14
2015-09-30 04:37:16| National Hurricane Center (East Pacific)
Issued at 1000 PM CDT TUE SEP 29 2015 000 WTPZ42 KNHC 300237 TCDEP2 TROPICAL STORM MARTY DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172015 1000 PM CDT TUE SEP 29 2015 After an unusually long convective burst that began around 1800 UTC, the convective pattern of Marty has deteriorated significantly over the past couple of hours. However, a 2306 UTC GPM microwave overpass indicated that Marty still had a 60-70 percent closed low-level eye with a diameter of 15 n mi. Based on the partial eye feature and a Dvorak classification of T3.0/45 kt from TAFB, the initial intensity is being maintained at 45 kt for this advisory. Microwave satellite images indicate that Marty has essentially been stationary since the previous advisory. However, as Marty's low-level and mid-/upper-level circulations begin to decouple during the next 12 hours or so due to increasing vertical wind shear, the cyclone is forecast to begin moving slowly westward tonight and on Wednesday under the influence of a weak low- to mid-level ridge located over central Mexico. Although the spread in the track guidance is fairly large, the models are in generally good agreement on a slow westward to west-northwestward motion throughout the forecast period. As a result, the official forecast track is similar to the previous advisory track, and lies close to the consensus models TVCE and GFEX. Despite strong shear conditions, the recent convective burst has been sustained by strong upper-level difluence created by southwesterly flow over the northwestern portion of the Marty's circulation and westerly flow over the southeastern portion of the circulation. However, this favorable upper-level pattern is expected to abate during the next 12 hours and be replaced by strong southwesterly unidirectional flow, which should create very unfavorable shear conditions across the cyclone. The result is that Marty should steadily or even rapidly weaken, becoming a tropical depression in about 24 hours, followed by degeneration into a remnant low by 36-48 hours. The NHC intensity forecast follows the weakening trend of the previous intensity forecast, and remains in agreement with the LGEM statistical-dynamical intensity model. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 16.3N 101.2W 45 KT 50 MPH 12H 30/1200Z 16.4N 101.8W 35 KT 40 MPH 24H 01/0000Z 16.6N 102.8W 30 KT 35 MPH 36H 01/1200Z 16.7N 104.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 02/0000Z 16.8N 105.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 03/0000Z 17.0N 107.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 04/0000Z 18.5N 109.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 05/0000Z...DISSIPATED $$ Forecaster Stewart
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