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Tropical Storm NORA Forecast Discussion Number 4
2015-10-10 10:43:57| National Hurricane Center (East Pacific)
Issued at 200 AM PDT SAT OCT 10 2015 000 WTPZ43 KNHC 100843 TCDEP3 TROPICAL STORM NORA DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182015 200 AM PDT SAT OCT 10 2015 Nora has changed little in organization during the past several hours. The low-level center continues to be near the southeastern edge of the convection, and the strongest convection is currently in outer bands well northwest of the center. This is likely due to the effects of light southeasterly vertical wind shear. In addition, recent ASCAT data suggests the circulation is elongated north to south. Satellite intensity estimates are 35 kt from both TAFB and SAB, and the ASCAT data also shows winds near 35 kt. Based on this, the advisory intensity remains 35 kt. Nora is now moving 285/14, with the cyclone continuing to be steered by a deep-layer subtropical ridge to the north. The dynamical models forecast the ridge to weaken during the next 36 hours, with Nora moving generally westward with a decrease in forward speed. After that time, the tropical cyclone is likely to turn northward and probably recurve as a deep-layer trough over the north Pacific breaks the subtropical ridge. The track guidance is tightly clustered for the first 36 hours, but subsequently there is an increased spread on where and how fast Nora will recurve. The ECMWF shows a weaker Nora moving farther west and eventually turning northward along 149W by 120 hours. The UKMET shows a stronger Nora making an earlier recurvature with the storm near 19N 138W by 120 hours. The GFS lies between these models and is near the center of the guidance envelope. The new track forecast is a little north of the previous forecast for the first 48 hours, and then it is a little west of the previous forecast after that time. The new track is near the center of the guidance envelope and lies a little west of the GFS after 72 hours. Nora is expected to remain in an environment of light shear and warm sea surface temperatures for the next 2-3 days, which should allow strengthening. After that, the cyclone is expected to encounter unfavorable conditions of strong southwesterly shear and decreasing sea surface temperatures. Based on this, the new intensity forecast follows the trend of the previous forecast in calling to Nora to peak as a hurricane in about 72 hours and subsequently weaken to a tropical storm by 120 hours. The new forecast is in best agreement with the Florida State Superensemble. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 11.6N 136.5W 35 KT 40 MPH 12H 10/1800Z 11.9N 138.3W 45 KT 50 MPH 24H 11/0600Z 12.1N 140.5W 50 KT 60 MPH 36H 11/1800Z 12.4N 142.3W 60 KT 70 MPH 48H 12/0600Z 12.7N 143.7W 65 KT 75 MPH 72H 13/0600Z 13.5N 145.5W 75 KT 85 MPH 96H 14/0600Z 16.0N 145.0W 70 KT 80 MPH 120H 15/0600Z 18.5N 142.5W 60 KT 70 MPH $$ Forecaster Beven
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