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Tropical Storm HILDA Forecast Discussion Number 7
2015-08-07 16:35:28| National Hurricane Center (East Pacific)
Issued at 800 AM PDT FRI AUG 07 2015 000 WTPZ45 KNHC 071435 TCDEP5 TROPICAL STORM HILDA DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102015 800 AM PDT FRI AUG 07 2015 Infrared satellite data, along with VIIRS moonlight visible imagery and a just received AMSR-2 overpass, show that Hilda is maintaining strong convection near the center. However, the system continues to have a sheared appearence, which is somewhat surprising since the available data show less than 10 kt of shear. The various satellite intensity estimates range between 45-55 kt, so the initial intensity remains 50 kt. The cirrus outflow is good to the west and poor to the east. The initial motion is 275/11. For the next 48-72 hours, Hilda should be steered westward to west-northwestward by the deep-layer subtropical ridge to its north. After that time, a mid- to upper-level low is expected to develop north of the Hawaiian Islands, which should cause Hilda to turn northwestward and north-northwestward. The track guidance again generally agrees on this scenario, but there remains a significant spread in how sharply Hilda will turn based on the strength of the cyclone after 72 hours. The GFS, GFDL, and GFDN, which depict a stronger cyclone, have sharper turns and end up on the east side of the guidance envelope. The ECMWF, HWRF, and GFS ensemble mean forecast a weaker Hilda, and they show a more westward motion. The UKMET and the various consensus models are between these extremes. The new forecast track, which is little changed from the previous track, follows this part of the guidance. The dynamical models are in good agreement that whatever shear is occurring should diminish in 24 hours or less. This should allow a faster rate of development, with Hilda forecast to become a hurricane in 24-36 hours and reach its peak intensity in 48-72 hours. After 72 hours, the cyclone is expected to encounter strong southwesterly vertical shear and decreasing sea surface temperatures, and this combination should cause significant weakening. The new intensity forecast has minor adjustments from the previous forecast and is in best overall agreement with the intensity consensus. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 12.8N 136.7W 50 KT 60 MPH 12H 08/0000Z 13.0N 138.3W 55 KT 65 MPH 24H 08/1200Z 13.6N 140.5W 60 KT 70 MPH 36H 09/0000Z 14.3N 142.5W 70 KT 80 MPH 48H 09/1200Z 15.1N 144.5W 75 KT 85 MPH 72H 10/1200Z 16.5N 147.5W 75 KT 85 MPH 96H 11/1200Z 18.5N 149.5W 55 KT 65 MPH 120H 12/1200Z 20.5N 150.5W 40 KT 45 MPH $$ Forecaster Beven
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