000 WTPZ45 KNHC 092059 TCDEP5 Tropical Storm Darby Discussion Number 1 NWS National Hurricane Center Miami FL EP052022 300 PM MDT Sat Jul 09 2022 The area of low pressure we have been monitoring well offshore the southwestern coast of Mexico has become much better organized on conventional satellite imagery throughout the day. The current structure on visible satellite imagery consists of a well-defined curved band to the north and west with what already appears to be a small central dense overcast forming near the estimated center. In fact, there is already a small dimple beginning to appear on the last few frames of visible satellite imagery which could be the initial indications that a small inner core is forming. While C-band scatterometer imagery (ASCAT-B/C) largely missed the small storm earlier today, there was a KU-band scatterometer late this morning that had enough non-rain contaminated vectors to indicate the system likely possesses a closed circulation. The subjective Dvorak classifications at 1800 UTC from TAFB/SAB were both T2.0/30 kt, but given the continued improvement on satellite imagery since then, advisories are being initiated on Tropical Storm Darby at this time, with winds of 35 kt. The current motion of Darby is just north of due west at 280/14 kt. A general due westward motion is expected over the next 24-48 h as the small storm is situated on the south side of a expansive deep-layer subtropical ridge centered over the southwestern United States. Towards the end of the forecast period, Darby will be approaching a weakness in this ridge, which may allow the storm to start gaining latitude after 48 hours. The initial track forecast of Darby is very close to the reliable track consensus aids, though is just a shade further north, in deference to both the GFS and ECMWF forecasts. The structure of Darby is quite impressive for a system that has only recently formed. In addition, both the GFS- and ECMWF-based SHIPS guidance indicate that the small storm will remain in a low shear (under 10 kt), warm sea-surface temperatures (above 28C), and sufficient mid-level moisture for the next 2-3 days. Assuming an inner core forms relatively soon, this environment likely favors quick intensification. In fact, the ECMWF SHIPS-RII guidance indicates a 44 percent chance of a 25 kt or higher increase in intensity over the next 24 hours. While the current NHC intensity forecast will not go that high quite yet, it does make Darby a hurricane in only 36 h. This intensity forecast is on the upper-end of the guidance envelope, but not far off the HFIP corrected consensus approach (HCCA) that is also near hurricane intensity in 36 h. Late in the forecast, Darby will likely encounter cooler ocean waters and much higher shear, which should begin to induce weakening by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 14.3N 113.5W 35 KT 40 MPH 12H 10/0600Z 14.4N 116.0W 45 KT 50 MPH 24H 10/1800Z 14.5N 118.8W 55 KT 65 MPH 36H 11/0600Z 14.4N 121.7W 65 KT 75 MPH 48H 11/1800Z 14.4N 124.3W 75 KT 85 MPH 60H 12/0600Z 14.6N 127.0W 80 KT 90 MPH 72H 12/1800Z 15.0N 129.2W 80 KT 90 MPH 96H 13/1800Z 16.2N 133.4W 65 KT 75 MPH 120H 14/1800Z 17.6N 138.4W 45 KT 50 MPH $$ Forecaster Papin