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| #796711 (Received by flhurricane at: 10:44 PM 19.Aug.2015) TCDAT4 TROPICAL STORM DANNY DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042015 1100 PM AST WED AUG 19 2015 Convection associated with Danny has increased in both coverage and organization during the past several hours. Overall, though, the storm still looks a little less organized than 24 hours ago. The various satellite intensity estimates are unchanged since the last advisory, so the initial intensity remains 45 kt. The cirrus outflow is good in the northern semicircle and poor elsewhere. Danny has turned to the right over the past several hours, and the initial motion is now 295/9. A weak subtropical ridge north of the cyclone is expected to steer Danny generally west-northwestward for the next couple of days. After that, the ridge is forecast to strengthen as a mid- to upper-level low currently near Bermuda lifts out to the north. This should cause Danny to turn more westward at a faster forward speed, with the center forecast to be near the Leeward Islands by 120 hours. There is some spread in the guidance during this time, with the UKMET, GFDN, GFDL and NAVGEM models showing a more northward motion than the other guidance. One change since the previous advisory is that the new GFS has shifted southward and now lies closer to the ECMWF forecast on the south side of the guidance envelope. The new track forecast, which is on the south side of the guidance near the ECMWF/GFS/HWRF/GFS Ensemble Mean solutions, is similar to the previous forecast. Earlier Windsat data shows that Danny has a well-defined inner core, and this, combined with a light-vertical wind shear environment, should allow strengthening for the next three days or so. However, experimental Saharan Air Layer (SAL) Meteosat imagery continues to show abundant dry air not far from the storm in the northern semicircle. Entrainment of this air is expected to limit intensification, and this is reflected by a downward trend in the intensity guidance. After 72 hours, the cyclone is expected to encounter even drier air and southwesterly shear, which should cause weakening. The new intensity forecast is identical to the previous forecast through 48 hours and then shows slightly lower intensities thereafter. It should be noted that the ECMWF and Canadian models forecast Danny to weaken to a tropical wave by 120 hours, which is a plausible alternative scenario given the forecast environment and the small size of the cyclone. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 12.1N 42.7W 45 KT 50 MPH 12H 20/1200Z 12.6N 43.9W 50 KT 60 MPH 24H 21/0000Z 13.1N 45.4W 55 KT 65 MPH 36H 21/1200Z 13.7N 47.0W 60 KT 70 MPH 48H 22/0000Z 14.4N 48.6W 65 KT 75 MPH 72H 23/0000Z 15.5N 53.0W 70 KT 80 MPH 96H 24/0000Z 16.0N 57.5W 65 KT 75 MPH 120H 25/0000Z 17.0N 62.5W 55 KT 65 MPH $$ Forecaster Beven |
