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Tropical Storm SIMON Forecast Discussion Number 19
2014-10-06 10:42:09| National Hurricane Center (East Pacific)
Issued at 200 AM PDT MON OCT 06 2014 000 WTPZ44 KNHC 060841 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 AM PDT MON OCT 06 2014 Simon's cloud pattern continues to deteroriate. Microwave data indicate that the cyclone's low-level center is exposed to the southwest of the main convective mass due to strong southwesterly vertical wind shear. The remaining central convection is no longer very deep either, with cloud top temperatures having risen to -50 to -60 deg C. A large plume of stratiform rain and high clouds also extends well north and east of the center, though even this area has been shrinking. The initial wind speed is reduced to 50 kt based on a blend of Final T-numbers of 3.0/45 kt and 3.5/55 kt from TAFB and SAB, respectively, which should provide a reasonable estimate of the intensity in cases of rapid weakening. Extremely strong west-southwesterly vertical shear of 30-40 kt will cause a decoupling of the cyclone during the next day or two, while very unfavorable thermodynamic conditions should result in a loss of deep convection. This should cause the rapid weakening trend observed during the past 24 hours to continue, and remnant low status is now predicted in 36 hours or perhaps sooner. The remnant circulation could dissipate prior to reaching the Baja California peninsula, as indicated by the latest SHIPS model output, or in the very least arrive in a greatly weakened state. The NHC wind speed forecast is largely an update of the previous one in agreement with the latest multi-model consensus. Simon has turned northward, or 360/06, around the western periphery of a subtropical ridge extending westward near the southwestern coast of Mexico. A shortwave trough moving toward southern California should turn the cyclone north-northeastward in the next 12 to 24 hours, but Simon will have just begun to recurve when it shears apart. The track guidance shows the remnant circulation continuing north-northeastward at varying forward speeds, with the GFS still much faster than the ECMWF and UKMET. The NHC track forecast is very near the previous one and the multi-model consensus through 48 hours but is slower after that time to acknowledge the possibility that a weaker system than depicted in global model fields might not reach the northern Baja California peninsula. Even if Simon or its remnant circulation does not make it across the rugged terrain of the Baja California peninsula, moisture associated with this system is expected to spread across the northern Baja California peninsula, northwestern Mexico, and into the U.S. Desert Southwest, which could trigger heavy rains in those regions during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 24.4N 117.6W 50 KT 60 MPH 12H 06/1800Z 25.3N 117.5W 40 KT 45 MPH 24H 07/0600Z 26.4N 117.0W 30 KT 35 MPH 36H 07/1800Z 27.6N 116.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 08/0600Z 28.8N 115.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 09/0600Z 30.2N 114.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 96H 10/0600Z...DISSIPATED $$ Forecaster Kimberlain
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