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Tropical Storm HILDA Forecast Discussion Number 6
2015-08-07 10:38:00| National Hurricane Center (East Pacific)
Issued at 200 AM PDT FRI AUG 07 2015 000 WTPZ45 KNHC 070837 TCDEP5 TROPICAL STORM HILDA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102015 200 AM PDT FRI AUG 07 2015 A GPM Microwave Imager pass from 0431 UTC revealed that Hilda's center was located just under the eastern edge of the deep convection due to some easterly shear. The overall cloud pattern has not really improved since earlier advisories, and the initial intensity remains 50 kt. This is supported by Dvorak estimates of T3.5/55 kt from TAFB and T3.0/45 kt from SAB. Although Hilda's intensity has been steady for the past 12 hours, easterly shear is relaxing, and the cyclone should be able to strengthen soon. Hilda is forecast to be in a low-shear environment and over sea surface temperatures of 27-29C during the next three days or so, during which time intensification is expected. On days 4 and 5, weakening is anticipated as southwesterly shear of 25-35 kt begins to affect the cyclone. The NHC intensity forecast is near the upper bound of the guidance and shows a peak intensity occurring in about 48 hours. Hilda is moving due west, or 270/11 kt. The cyclone should turn west-northwestward by 36 hours as it approaches a weakness in the subtropical ridge. Then, a mid- to upper-level low is expected to develop north of the Hawaiian Islands in about three days, which should cause Hilda to turn northwestward and north-northwestward on days 4 and 5. The track guidance generally agrees on this scenario, but there is significant discrepancy on how sharply Hilda will turn after 72 hours. The GFS and GFDL, which depict a stronger cyclone, have sharper turns and end up on the east side of the guidance envelope. The ECMWF, on the other hand, does not intensify Hilda as much and is well to the west of the other track models. The updated NHC track forecast shows a sharper turn than in the previous advisory, but the turn is not nearly as sharp as suggested by the GFS, GFDL, and the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 12.6N 135.6W 50 KT 60 MPH 12H 07/1800Z 12.8N 137.3W 60 KT 70 MPH 24H 08/0600Z 13.2N 139.3W 65 KT 75 MPH 36H 08/1800Z 13.9N 141.3W 70 KT 80 MPH 48H 09/0600Z 14.7N 143.3W 75 KT 85 MPH 72H 10/0600Z 16.1N 147.1W 70 KT 80 MPH 96H 11/0600Z 18.0N 149.0W 60 KT 70 MPH 120H 12/0600Z 20.5N 150.0W 45 KT 50 MPH $$ Forecaster Berg
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