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Tropical Storm Hilda Forecast Discussion Number 15
2021-08-03 11:00:05| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Tue Aug 03 2021 000 WTPZ43 KNHC 030900 TCDEP3 Tropical Storm Hilda Discussion Number 15 NWS National Hurricane Center Miami FL EP082021 200 AM PDT Tue Aug 03 2021 Overnight, Hilda's deep convection has continued to pulse, but primarily in the southern semicircle of the circulation as 15-20 kt of northeasterly vertical wind shear continues displacing this activity downshear. A helpful ASCAT-B pass at 0602 UTC indicated the center of Hilda was located on the northern edge of the convective cirrus canopy, with the instrument also indicating a peak wind retrieval of 53 kt. The most recent microwave imagery concurs with this assessment and also indicates the earlier eyewall is no longer well-defined. While the 0600 UTC subjective Dvorak estimates from TAFB and SAB were both T4.0/65 kt, the most recent objective Dvorak estimate from UW-CIMSS was down to T3.5/55 kt. Given the devolving convective structure seen on microwave, the initial intensity has been reduced to 60 kt, leaning towards the lower intensity estimates. Hilda continues to move slowly northwestward, at 315/7 kt as it remains positioned southwest of a mid-level ridge centered over southern California. Over the next several days, this ridge is forecast to build westward over the East Pacific as a short-wave trough offshore of California lifts out. This synoptic pattern should allow Hilda to gradually bend to the west-northwest and increase its forward motion slightly over the forecast period. Hilda will also become increasingly influenced by low-level ridging, steering the cyclone more westward as it becomes a weak and shallow cyclone. The latest NHC track forecast is just a touch south of the previous forecast track, blending the reliable TVCE and HCCA consensus aids. Northeasterly vertical wind shear, related to the remaining convective outflow of Ignacio, is expected to keep Hilda on a weakening trend over the next day or so. Even though this shear is expected to subside thereafter, Hilda will also be crossing the 25 degree Celsius sea-surface temperature isotherm in 24 hours. Thus, continued weakening is expected. The latest NHC intensity forecast follows the HCCA consensus aid closely, showing weakening throughout the forecast period. The tropical cyclone is now expected to degenerate to a remnant low by Friday, when model guidance suggests organized deep-convection will cease. The remnant low is then expected to open up into a trough by the weekend, well east of Hawaii. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 17.0N 123.9W 60 KT 70 MPH 12H 03/1800Z 17.6N 124.6W 50 KT 60 MPH 24H 04/0600Z 18.6N 125.5W 45 KT 50 MPH 36H 04/1800Z 19.4N 126.7W 40 KT 45 MPH 48H 05/0600Z 20.2N 128.1W 35 KT 40 MPH 60H 05/1800Z 21.0N 129.9W 30 KT 35 MPH 72H 06/0600Z 21.7N 132.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 07/0600Z 22.4N 136.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 08/0600Z...DISSIPATED $$ Forecaster Papin/Brown
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