ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM TROPICAL STORM MARTY DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP172015 400 AM CDT SUN SEP 27 2015 ASCAT data from a few hours ago indicate that Marty's maximum winds have increased to 45 kt. The center is embedded beneath a persistent burst of deep convection, and strong convective bands trail to the south and southwest of the central dense overcast. The structure suggests there could be a little bit of westerly shear, which UW-CIMSS and the SHIPS diagnostics are showing to be about 10-15 kt. Marty is over sea surface temperatures of at least 30 degrees Celsius, and the vertical shear is expected to be steady for the next 24 hours or so. These conditions should allow the cyclone to continue strengthening, and in fact, rapid intensification is a possibility. The SHIPS RI guidance is showing a 64 percent chance of a 25-kt increase in winds during the next 24 hours, and the SHIPS and LGEM models bring Marty at or just below hurricane intensity at that time. The dynamical models are a little bit less aggressive with the future intensity, but given that Marty is already a little stronger from the get-go, the more aggressive statistical guidance seems to be the more likely scenario. Vertical shear is expected to increase by 36 hours, which is expected to lead to a quick weakening trend during the latter part of the forecast period. The updated NHC intensity forecast is adjusted upward a bit through 48 hours to account for the higher initial intensity and the latest guidance, and is actually very similar to the Florida State Superensemble. Marty is located to the west of a mid-level ridge which extends across Central America, and to the south of a deep-layer trough located over Mexico and the southern United States. This pattern is steering the cyclone northward, or 360/5 kt. Marty should turn northeastward but slow down during the next 48 hours as the steering currents weaken. After the vertical shear increases, possibly displacing the deep convection away from the center, the circulation is expected to stall and then turn westward between days 3 through 5, keeping the center just offshore of the coast of Mexico. The GFS and the NAVGEM are the only models that bring Marty inland over Mexico, but these solutions do not appear likely at this time, especially since even the GFS ensemble mean stays offshore. Despite these model differences, no significant changes were required to the NHC track forecast from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 14.3N 103.1W 45 KT 50 MPH 12H 27/1800Z 15.0N 102.9W 55 KT 65 MPH 24H 28/0600Z 15.6N 102.5W 65 KT 75 MPH 36H 28/1800Z 16.0N 102.1W 65 KT 75 MPH 48H 29/0600Z 16.2N 101.8W 60 KT 70 MPH 72H 30/0600Z 16.5N 101.6W 40 KT 45 MPH 96H 01/0600Z 17.0N 103.0W 30 KT 35 MPH 120H 02/0600Z 16.5N 105.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg NNNN
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Page last modified: Thursday, 31-Dec-2015 12:09:52 UTC