000 WTPZ45 KNHC 111454 TCDEP5 Hurricane Darby Discussion Number 9 NWS National Hurricane Center Miami FL EP052022 500 AM HST Mon Jul 11 2022 What a difference 24 hours makes! Darby has been rapidly intensifying for the last 12-18 hours, with the eye continuing to clear out on GOES-17 infrared satellite imagery surrounded by a thick ring of cold -65 to -75C cloud top temperatures. It is clear that the tropical cyclone was able to mix out the remaining dry air near its center last night and the last several microwave passes from GMI at 0732 UTC and AMSR2 at 0959 UTC have an impressive presentation with a thick ring of eyewall convection on the 89-GHz channel. Subjective Dvorak satellite estimates from TAFB and SAB are constrained due to Dvorak rules, but their data-T numbers were both T5.5/102 kt. The most recent CI number from the UW-CIMSS objective Advanced Dvorak Technique (ADT) was at T6.0/115 kt. Favoring the higher ADT estimate more, the current intensity is set to 110 kt, though this could be conservative. There are no obvious signs currently that would prevent Darby from intensifying further. There are few indications that an eyewall replacement cycle is imminent from the earlier microwave imagery and SHIPS guidance indicates the storm remains in a very low shear (near 5 kt) environment and over sufficently warm sea-surface temperatures (27-28 C). Thus, rapid intensification is forecast to continue over the next 12 h, and the NHC foreast intensity peaks Darby at 120 kt, which matches the latest ECMWF- and GFS-based SHIPS which have correctly been on the high side of the guidance envelope. After 36 hours, Darby is expected to move into sub 26C SSTs, and westerly shear is forecast to increase between 48-72 hours. Thus, the small vortex of Darby could weaken rapidly after 36 hours, with the latest intensity forecast still making the system a post-tropical cyclone at the end of the forecast period. Darby is continuing westward along at the same general speed and heading at 270/13 kt, steered primarily by a mid-level ridge centered to its north. The hurricane is expected to approach a slight weakness in the ridge after 24 hours, allowing the cyclone to gradually shift to a more west-northwestward track between 36-72 hours. However, by the end of the forecast period, as Darby becomes shallow vortex, its track will likely bend back westward as the low-level trade wind flow becomes dominant. The latest track forecast is not all that different from the previous one, choosing to remain close to a consensus of the GFS and ECMWF forecasts (GEFX) which remains just a bit north of the consensus aids HCCA and TVCE, which are influenced by the further south tracks of the weaker HWRF/HMON/UKMET guidance. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 14.6N 123.4W 110 KT 125 MPH 12H 12/0000Z 14.7N 125.6W 120 KT 140 MPH 24H 12/1200Z 14.8N 128.1W 120 KT 140 MPH 36H 13/0000Z 15.0N 130.5W 105 KT 120 MPH 48H 13/1200Z 15.4N 133.2W 85 KT 100 MPH 60H 14/0000Z 15.9N 135.8W 70 KT 80 MPH 72H 14/1200Z 16.7N 138.5W 55 KT 65 MPH 96H 15/1200Z 17.5N 143.3W 35 KT 40 MPH 120H 16/1200Z 17.3N 149.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Papin