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Tropical Storm Hilda Forecast Discussion Number 5
2021-07-31 22:36:19| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Sat Jul 31 2021 000 WTPZ43 KNHC 312036 TCDEP3 Tropical Storm Hilda Discussion Number 5 NWS National Hurricane Center Miami FL EP082021 200 PM PDT Sat Jul 31 2021 After strengthening quickly overnight and early this morning, Hilda's intensity appears to have leveled off for now. There continues to be hints of an eye feature in satellite images and deep convection is organized in curved bands around that feature. The latest Dvorak estimates are 3.5/55 kt from TAFB, 4.0/65 kt from SAB, and 4.1/67 kt from CIMSS at the University of Wisconsin. A recent ASCAT-B overpass showed a maximum wind of around 50 kt southeast of the center, but the coarse resolution of the instrument is unlikely to capture the storm's true intensity. Based on a combination of this data, the initial intensity is held at 60 kt, but this could be a little conservative and Hilda is very near hurricane strength. The aforementioned ASCAT data was also used to adjust the wind radii inward at the initial and short range forecast times. Steady strengthening seems likely during the next 24 to 36 hours as the environment remains generally favorable, consisting of relatively warm SSTs, low wind shear, and a high amount of moisture. The NHC intensity forecast during that time period is the same as before and lies at the high end of the model guidance, near HCCA. Beyond 36 hours, however, decreasing moisture and progressively cooler SSTs should end the strengthening trend and gradually cause weakening during the remainder of the forecast period. The NHC intensity forecast lies near the middle of the guidance envelope for that portion of the forecast. Hilda is moving west-northwestward at 12 kt. A subtropical ridge should keep the storm on a general west-northwest heading during the next several days, but the more skillful models like the GFS and ECMWF show some interaction with Tropical Depression Nine-E to the west and a low pressure area to the east. These interactions will likely cause some slow downs and an erratic motion at times during the forecast period. There continues to be a fair amount of spread in the models, especially in terms of forward speed, and the new forecast is a little to the north of the previous based on the latest guidance. This track prediction is slightly slower than the consensus aids, and has given more weight to the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 14.1N 117.9W 60 KT 70 MPH 12H 01/0600Z 14.5N 119.3W 70 KT 80 MPH 24H 01/1800Z 15.0N 121.0W 80 KT 90 MPH 36H 02/0600Z 15.5N 122.5W 85 KT 100 MPH 48H 02/1800Z 16.0N 123.8W 80 KT 90 MPH 60H 03/0600Z 16.8N 125.1W 75 KT 85 MPH 72H 03/1800Z 17.8N 126.7W 65 KT 75 MPH 96H 04/1800Z 19.3N 129.8W 50 KT 60 MPH 120H 05/1800Z 20.4N 133.7W 40 KT 45 MPH $$ Forecaster Cangialosi
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