ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM MARTY DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172015 1000 AM CDT TUE SEP 29 2015 Satellite imagery and data from the Mexican radar at Acapulco indicate that Marty continues to lose organization due to the effects of 30 kt of westerly shear. The convection is occurring in episodic bursts, and the low-level center is located near the southwestern edge of the bursts. The initial intensity is decreased to 50 kt based on 1200 UTC satellite intensity estimates from TAFB and SAB and the subsequent decay in the cloud pattern. Marty continues to drift erratically with the initial motion now 120/3. The mid- to upper-level trough north of the system is starting to weaken and split, with an upper-level low developing northwest of Marty and a mid-level ridge developing north of the storm. This evolution should result in Marty beginning a west- northwestward to westward motion during the next 24-48 hours, and all the guidance that does not quickly dissipate the cyclone supports this scenario. The new forecast track is a little south of the previous track based on the initial position, and it is also faster in moving Marty westward. However, it is slower than the model consensus. On the new forecast track, it is less likely that the center of Marty will make landfall on the coast of Mexico. The dynamical models forecast the current shear to continue for the next 36-48 hours, which should cause Marty to steadily, if not rapidly, weaken. The new intensity forecast, which is in best agreement with the LGEM model, is an update of the previous forecast in calling for Marty to weaken to a tropical depression in 24-36 hours and then degenerate into a remnant low by 48 hours. It should be noted that this forecast lies on the upper edge of the intensity guidance envelope, so Marty could weaken faster than currently forecast. One extra day has been added to the remnant low phase based on the forecasts from the ECMWF, UKMET, and Canadian models. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 16.2N 101.6W 50 KT 60 MPH 12H 30/0000Z 16.4N 101.6W 45 KT 50 MPH 24H 30/1200Z 16.6N 102.2W 35 KT 40 MPH 36H 01/0000Z 16.8N 103.3W 30 KT 35 MPH 48H 01/1200Z 16.9N 104.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/1200Z 17.0N 106.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 03/1200Z 17.0N 107.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 04/1200Z...DISSIPATED $$ Forecaster Beven NNNN
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Page last modified: Thursday, 31-Dec-2015 12:09:52 UTC