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| #796622 (Received by flhurricane at: 4:35 PM 19.Aug.2015) TCDAT4 TROPICAL STORM DANNY DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042015 500 PM AST WED AUG 19 2015 Satellite imagery shows that Danny's deep convection collapsed late this morning, with the experimental Saharan Air Layer (SAL) Meteosat imagery suggesting that dry-air entrainment could be the cause. Although visible satellite pictures still show a vigorous circulation and some renewed convection, the system overall has lost organization and become more embedded in the Intertropical Convergence Zone since yesterday. With little change in the Dvorak classifications, the initial intensity is kept at 45 kt in agreement with the latest CI number from TAFB. Given the current appearance of the cyclone, it might be that dry air associated with the SAL intruding from the north and west has become a greater impediment to intensification. Dry air aside, other atmospheric parameters governing intensification would seem to favor some strengthening during the next 2 to 3 days, and the official forecast shows modest strengthening. After that time, significantly drier mid-tropospheric air and an increase in westerly flow aloft associated with an enhanced and persistent mid-oceanic trough across the Caribbean region is expected to induce weakening as shown in the ECWMF solution. There is a large discrepancy between the statistical and dynamical model guidance, with the GFS-based statistical guidance continuing to show more intensification and the regional hurricane models showing only modest strengthening followed by weakening. The official intensity forecast is similar to but a little lower than the previous one at later times, consistent with the multi-model consensus. The cyclone has been moving generally west but at a slower forward speed (280/08) in response to a weakening subtropical ridge to the north of the cyclone. A west-northwestward motion is expected during the next next 2 to 3 days, at which time an interesting split in the model guidance occurs. The GFS shows a much stronger representation of Danny moving west-northwestward near and north of the Greater Antilles in 3 to 5 days. The ECWMF solution, on the other hand, depicts Danny as a shallower feature from the start and as a weakening cyclone as it nears the Lesser Antilles on a westward track. The new forecast track maintains the philosophy of the previous one by showing a general westward track in the extended range, giving more weight to the ECMWF solution that shows weakening. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 11.5N 42.0W 45 KT 50 MPH 12H 20/0600Z 12.1N 43.2W 50 KT 60 MPH 24H 20/1800Z 12.6N 44.8W 55 KT 65 MPH 36H 21/0600Z 13.1N 46.3W 60 KT 70 MPH 48H 21/1800Z 13.8N 47.9W 65 KT 75 MPH 72H 22/1800Z 15.0N 51.8W 75 KT 85 MPH 96H 23/1800Z 16.0N 56.9W 70 KT 80 MPH 120H 24/1800Z 16.8N 62.0W 60 KT 70 MPH $$ Forecaster Kimberlain |
