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| #800910 (Received by flhurricane at: 10:38 PM 04.Sep.2015) TCDAT1 TROPICAL STORM FRED DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062015 1100 PM AST FRI SEP 04 2015 An ASCAT-A pass just before 0000 UTC showed a small area of 35-kt winds northeast of Fred's center, and that is the basis for the initial intensity, making Fred a tropical storm once again. The central pressure has been adjusted upward to 1009 mb based on observations from drifting buoy 13519, as it appears Fred is now embedded in an environment of higher pressure. Despite rather hostile vertical shear, Fred has managed to maintain enough organized deep convection during the past couple of days to stave off post-tropical status. The latest burst of convection is now moving away from the low-level center, but this bursting pattern seems likely to continue for the next couple of days as the cyclone moves over gradually warmer waters in moderate to strong shear. Since Fred has survived this long, it seems less likely that the cyclone will become post-tropical in the short term, and that is no longer shown in the official forecast. However, given our limited ability to predict convective scale changes, this still remains a possibility. Little significant change in intensity is shown in the first 48 hours, as the guidance shows Fred between 30 and 35 kt during that time. Subsequently, as the shear weakens all of the guidance shows at least some strengthening. The NHC forecast shows only a modest re-intensification later in the period, given the possibility that the circulation of Fred could open up or be absorbed in 4 or 5 days as shown by the GFS and ECMWF models. The initial motion estimate is 290/09, and Fred should begin to move around the western periphery of the subtropical ridge during the next couple of days and then turn northeastward in the mid-latitude westerlies. This cycle the models have trended faster with the forward speed of Fred, and have shown a northward shift after 48 hours. The NHC forecast has been adjusted to account for these trends, but now lies on the right side of the guidance envelope at days 3 through 5. Given the large spread at these time ranges, and the possibility that Fred could be absorbed or dissipate late in the period, the extended portion of the track forecast is of lower than normal confidence. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 22.8N 40.1W 35 KT 40 MPH 12H 05/1200Z 23.2N 41.1W 35 KT 40 MPH 24H 06/0000Z 23.9N 42.2W 30 KT 35 MPH 36H 06/1200Z 25.3N 42.7W 30 KT 35 MPH 48H 07/0000Z 27.1N 41.7W 30 KT 35 MPH 72H 08/0000Z 30.5N 38.0W 35 KT 40 MPH 96H 09/0000Z 34.5N 33.5W 35 KT 40 MPH 120H 10/0000Z 36.0N 30.5W 35 KT 40 MPH $$ Forecaster Brennan |
