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#801361 (Received by flhurricane at: 4:44 PM 06.Sep.2015) TCDAT2 TROPICAL STORM GRACE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072015 500 PM AST SUN SEP 06 2015 Grace is a fairly well-organized, compact tropical cyclone with banding features and well-defined upper-level outflow to the north and south of the system. Deep convection has been rather limited today, but recent imagery shows some cold cloud tops developing near the center. The current intensity is set to 45 kt in agreement with a subjective Dvorak estimate from TAFB. Since the vertical wind shear is expected to remain modest for the next 24 hours or so, there is window of opportunity for short-term strengthening. Within 36 hours, the dynamical guidance shows the shear increasing to over 20 kt, and this should cause a weakening trend beginning around that time. The official intensity forecast is a little above the model consensus for the first half of the period and close to, or a little below, the consensus thereafter. It is worth noting that the GFS shows significant weakening of the cyclone in 4 to 5 days, with the ECMWF showing dissipation by that time. The storm has accelerated a bit and is now moving at about 280/13. For the next several days, Grace should continue to move within a moderate low- to mid-level easterly flow on the south side of the subtropical ridge. The track guidance models are noticeably faster than they were on the previous cycle, so the official forecast is adjusted accordingly. The NHC track is not far from the latest dynamical model consensus, TVCN. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 13.2N 31.2W 45 KT 50 MPH 12H 07/0600Z 13.3N 33.3W 50 KT 60 MPH 24H 07/1800Z 13.6N 36.2W 55 KT 65 MPH 36H 08/0600Z 13.9N 39.1W 55 KT 65 MPH 48H 08/1800Z 14.3N 42.1W 50 KT 60 MPH 72H 09/1800Z 15.0N 48.5W 45 KT 50 MPH 96H 10/1800Z 16.0N 55.0W 40 KT 45 MPH 120H 11/1800Z 17.0N 61.0W 30 KT 35 MPH $$ Forecaster Pasch |