000 WTPZ45 KNHC 102037 TCDEP5 Tropical Storm Darby Discussion Number 5 NWS National Hurricane Center Miami FL EP052022 1100 AM HST Sun Jul 10 2022 Darby is a small but fairly well-organized tropical cyclone. 1-minute GOES-17 imagery has been quite helpful to diagnose the system's structure, which consists of a handful of curved bands around the periphery of the circulation, with pulsing convection near the center that has, at times, wrapped nearly all the way around. Earlier microwave imagery showed hints that Darby was starting to mix-out some of the dry-air entrainment that was noticed this morning, with even a hint of a mid-level eye becoming evident on an SSMIS 91-GHz microwave channel at 1421 UTC. The latest subjective Dvorak intensity estimates were a consensus CI 3.5/55-kt, which is the basis for Darby's current intensity this advisory. Over the next 36-48 hours, the biggest question related to Darby's future intensity is just how effective the tropical cyclone will be at preventing additional dry-air intrusions into its inner core. Because the system has a very small core, it could be prone to rapid intensity changes, both up and down, even due to seemingly small fluctuations to its larger-scale environment. While SHIPS guidance indicates that the deep-layer 200-850 mb shear should remain under 10 kt for the next 48 hours, the direction of the shear vector is from the north, where there is drier mid-level air. In addition, there is some sneaky higher northerly mid-level shear that may have played a role in dry air disrupting the convective structure of Darby last night and this morning. In any event, assuming the TC is able to close off its tiny inner core, at least steady intensification is still anticipated in the short-term. The latest NHC intensity forecast still peaks Darby as an upper-end Category 1 hurricane by 48 hours, which is on the high end of the guidance, but closest to the latest SHIPS forecast. Afterwards, northwesterly shear increases, helping to import even drier mid-level air, and sea-surface temperatures decrease below 26 C, which will likely lead to rapid weakening of the small system towards the end of the forecast period. The latest forecast now indicates Darby becoming a post-tropical remnant low in 120 hours, not long after it crosses the 140-degree longitude. Darby remains on a due westward heading at 270/14 kt. The cyclone continues to be steered westward by a prominent mid-level ridge to its north. By 36 hours though, Darby will begin to approach a weakness in this mid-level ridge, which should allow the system to begin gaining latitude. While the track guidance continues to exhibit relatively low across-track spread, there is substantially more along-track spread between the various deterministic members. Notably, the UKMET continues to be on the fast-leftward end of the guidance envelope, which does not seem realistic since Darby is more vertically deep than that model currently depicts. The latest track forecast continues to place more emphasis on the slower and stronger guidance, notably the GFS and ECMWF forecasts, which results in the track forecast being a little slower and a bit further north than the reliable guidance aids HCCA and TVCE. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 14.4N 119.1W 55 KT 65 MPH 12H 11/0600Z 14.5N 121.1W 65 KT 75 MPH 24H 11/1800Z 14.6N 123.7W 75 KT 85 MPH 36H 12/0600Z 14.8N 126.2W 80 KT 90 MPH 48H 12/1800Z 15.0N 128.7W 80 KT 90 MPH 60H 13/0600Z 15.5N 131.4W 70 KT 80 MPH 72H 13/1800Z 16.2N 133.8W 60 KT 70 MPH 96H 14/1800Z 17.8N 138.7W 40 KT 45 MPH 120H 15/1800Z 18.5N 144.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Papin