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Tropical Storm NORBERT Forecast Discussion Number 3
2014-09-03 04:39:46| National Hurricane Center (East Pacific)
Issued at 800 PM PDT TUE SEP 02 2014 000 WTPZ44 KNHC 030239 TCDEP4 TROPICAL STORM NORBERT DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 PM PDT TUE SEP 02 2014 Norbert has continued to slowly become better organized over the past few hours. Deep convection has increase near the center in a CDO-like feature, and a curved convective band extends into the western semicircle. The initial intensity of 40 kt is based on a blend of the latest subjective and objective Dvorak estimates, and this could be a bit conservative. The SHIPS model shows some moderate northeasterly to easterly shear over the cyclone for the next 2 to 3 days, but otherwise conditions appear favorable for strengthening. There is a fair bit of spread in the intensity guidance, in part due to variability in the track forecast. The HWRF model now shows the cyclone moving over the Baja peninsula, and has trended a bit weaker. On the other hand, the SHIPS model now shows Norbert becoming a hurricane in 36 to 48 hours. The new NHC track takes Norbert over warmer SSTs closer to the Baja peninsula in 2 to 3 days and the NHC intensity forecast has been adjusted upward, showing Norbert becoming a hurricane in 48 hours. This forecast is close to the SHIPS model and the FSU Superensemble. Gradual weakening is forecast at days 3 through 5 as the cyclone moves over cooler waters. Norbert has turned toward the left during the past few hours, with an initial motion estimate of 330/07. The dominant steering mechanism through the period will be a mid-level ridge centered over the southern United States, which should generally steer Norbert northwestward during the next 72 hours and then west-northwestward. Much of the track model guidance has shifted well to the right, or north, for this forecast cycle, especially at 48 hours and beyond. The GFS, GEFS ensemble mean, HWRF, and GFDL are now north of the ECMWF, which was previously along the right side of the guidance envelope. This shift appears to be due to a deeper representation of Norbert and more erosion of the subtropical ridge to the north. The NHC track has been shifted to the right this cycle, and now lies south of the multi-model consensus aid TVCE. The NHC track is close to a blend of the GFS and ECMWF through 36 hours and is a little south of that model blend afterward. Given the large shift in the guidance and the large spread, confidence in the track forecast is lower than normal and additional adjustments may be needed in future forecast cycles. The rightward shift in the track increases the threat to the southern part of the Baja California peninsula. A tropical storm or hurricane warning could be needed for this area tonight or early Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 19.2N 106.9W 40 KT 45 MPH 12H 03/1200Z 19.8N 107.8W 50 KT 60 MPH 24H 04/0000Z 20.4N 108.9W 55 KT 65 MPH 36H 04/1200Z 21.1N 109.8W 60 KT 70 MPH 48H 05/0000Z 21.9N 110.7W 65 KT 75 MPH 72H 06/0000Z 23.5N 112.8W 60 KT 70 MPH 96H 07/0000Z 24.5N 115.0W 50 KT 60 MPH 120H 08/0000Z 25.3N 117.0W 40 KT 45 MPH $$ Forecaster Brennan
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