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| #797578 (Received by flhurricane at: 4:59 AM 23.Aug.2015) TCDAT4 TROPICAL STORM DANNY DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042015 500 AM AST SUN AUG 23 2015 Satellite imagery and data from a NOAA Hurricane Hunter aircraft indicate that Danny has changed little since the previous advisory. Although the center is partly exposed on the southern edge of the deep convection, satellite images and data from the NOAA Hurricane Hunters and an earlier Gulfstream-IV synoptic mission indicate that Danny remains a well-defined and vertically deep system through at least the 400-mb level. Danny is moving westward and has maintained its previous motion of 275/13 kt. The track forecast reasoning remains basically unchanged from the previous advisory, but the new forecast track is heavily dependent on Danny remaining a tropical cyclone as it moves through the Leeward Islands and the northeastern Caribbean Sea. The model guidance, especially the GFS and ECMWF, made a significant southward shift on the latest cycle due to those models weakening the cyclone fairly quickly after 24 hours, with Danny becoming a vertically shallow remnant low that then moves westward within the easterly trade wind flow and into the Caribbean Sea by 36 hours. Given that the 18-20 kt of south-southwesterly vertical wind shear that is currently affecting the cyclone is not expected to change during the next 48 hours, Danny is forecast to be a tropical cyclone during that time and and not weaken as much of the global models are suggesting. As a result, Danny is forecast remain north of the GFEX and TVCN model consensus model tracks, and begin to make a turn toward the west-northwest after 24 hours. The NHC track forecast was nudged a little south of the previous advisory track, mainly due to the slight southerly initial position. As previously mentioned, the current environmental conditions that Danny is experiencing are forecast by the SHIPS intensity model to continue for the next 48 hours, which means that Danny should remain a small and sheared tropical cyclone during that time. The official intensity forecast still calls for Danny to weaken to a tropical depression in 36-48 hours as it passes near or south of the Virgin Islands and Puerto Rico. Danny is expected to become a remnant low in 72 hours and dissipate by 120 hours, but interaction with the land masses of Puerto Rico and/or Hispaniola could result in Danny dissipating sooner than forecast. Additional watches or warnings could be required for the Virgin Islands and Puerto Rico later this morning if Danny does not weaken as quickly as forecast or if the forecast track is not shifted farther south on subsequent advisories. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 15.8N 56.0W 50 KT 60 MPH 12H 23/1800Z 16.0N 58.0W 40 KT 45 MPH 24H 24/0600Z 16.5N 60.5W 35 KT 40 MPH 36H 24/1800Z 17.1N 63.1W 30 KT 35 MPH 48H 25/0600Z 17.8N 65.6W 30 KT 35 MPH 72H 26/0600Z 19.6N 70.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 27/0600Z 21.3N 75.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 28/0600Z...DISSIPATED $$ Forecaster Stewart |
