ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM NORBERT DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014 800 AM PDT SUN SEP 07 2014 Deep convection has been decreasing quickly during the last several hours, and only a small area of cold cloud tops remains to the south of the center. Satellite intensity estimates are falling, and the initial wind speed is lowered to 50 kt using an average of the Dvorak CI-numbers from TAFB, SAB, and UW-CIMSS. The quick weakening of Norbert is due to the influence of cool waters of around 25 C and a dry stable air mass. These factors will become even more unfavorable along the expected track of Norbert, and should cause the cyclone to degenerate to a remnant low in about 24 hours, or maybe even sooner. Once Norbert becomes a remnant low, the cyclone is expected to slowly spin down and then open into a trough in about 4 days. The NHC intensity forecast is lower than the previous one, mainly due to the observed rate of weakening. Norbert is still moving west-northwestward, but it is expected to turn toward the northwest and then north during the next day or so when it feels the influence of a deep-layer trough west of California. A slow down and turn toward the northeast or east is expected after that time when the shallow system is steered by the low-level flow toward the Baja California peninsula. No significant change was made to the previous track forecast, and it lies close to the GFS/ECMWF consensus. Although the system is weakening quickly, tropical moisture associated with Norbert and the Pacific ITCZ will continue to spread northward across northern Mexico and the southwestern United States. This could result in heavy rains and life-threatening flash flooding in these area during the next day or two. Please see information from your local weather office for more details. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 26.0N 117.0W 50 KT 60 MPH 12H 08/0000Z 26.9N 117.7W 35 KT 40 MPH 24H 08/1200Z 27.9N 118.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 09/0000Z 28.5N 118.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 09/1200Z 29.1N 117.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 10/1200Z 29.5N 116.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 11/1200Z...DISSIPATED $$ Forecaster Cangialosi NNNN
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