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Tropical Storm SIMON Forecast Discussion Number 24

2014-10-07 16:36:51| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE OCT 07 2014 000 WTPZ44 KNHC 071436 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 24 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 AM PDT TUE OCT 07 2014 The deep convection associated with Simon has diminished even further, with only a small patch of showers remaining near the north-central Baja California peninsula. Unless significant convection returns to the circulation later today, the cyclone could degenerate into a remnant low by tonight. The intensity is maintained at 35 kt for now, based mainly on continuity from the earlier ASCAT pass. The surface circulation of Simon or its remnant low is likely to dissipate while it moves into the southwestern United States, unless it fails to survive its passage over the mountainous Baja peninsula during the next day or so. The motion is just slightly faster than before, or 025/8 kt. With the cyclone expected to remain embedded in low- to mid-level south-southwesterly flow, this motion should continue until the system loses its identity. The official forecast is close to TVCN, the dynamical model consensus. 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. Please refer to statements from your local weather office for information on hazards specific to your area. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 27.7N 116.7W 35 KT 40 MPH 12H 08/0000Z 28.7N 116.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 08/1200Z 30.0N 115.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 09/0000Z 31.8N 113.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 09/1200Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm SIMON Forecast Discussion Number 22

2014-10-07 04:43:19| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON OCT 06 2014 000 WTPZ44 KNHC 070243 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 PM PDT MON OCT 06 2014 The cloud pattern of Simon has changed little since the previous advisory. The tropical cyclone continues to produce a small area of deep convection well to the north of the exposed low-level center. Subjective satellite intensity estimates continue to slowly decrease and the initial wind speed has been lowered to 40 kt for this advisory. Westerly shear of 30 kt or more, along with cool water, and a drier mid-level atmosphere should cause the tropical storm to weaken during the next day or so. Simon is expected to degenerate into a post-tropical cyclone by late Tuesday and dissipate within 2 to 3 days. The latest satellite fixes indicate that Simon has turned north-northeastward or 015/7 kt. Simon should move north- northeastward to northeastward in southwesterly flow between a mid-level ridge to its southeast and an approaching mid-latitude trough. The NHC track forecast lies between the ECMWF and the more poleward GFS. The new track is close to the previous advisory through 24 hours, but has been adjusted a little northward thereafter. 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. Please refer to statements from your local weather office for information on hazards specific to your area. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 26.5N 117.2W 40 KT 45 MPH 12H 07/1200Z 27.5N 116.7W 30 KT 35 MPH 24H 08/0000Z 28.7N 116.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 08/1200Z 29.8N 115.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 09/0000Z 30.9N 114.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 10/0000Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm SIMON Forecast Discussion Number 21

2014-10-06 22:44:47| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON OCT 06 2014 000 WTPZ44 KNHC 062044 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 21 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 PM PDT MON OCT 06 2014 Although the tropical cyclone has very little deep convection remaining, a recent ASCAT overpass indicated that the system had not weakened as much as earlier estimated. Data from that pass showed that the current intensity is about 45 kt. Water vapor imagery shows quite a bit of southwesterly shear affecting Simon at this time, and dynamical models show the shear becoming even stronger within a day or two. The official intensity forecast is above most of the numerical guidance and shows the system degenerating into a remnant low in 24 hours. However, since the ASCAT data revealed a slightly larger and stronger cyclone, and considering the uncertainties in the forecast track, it is prudent to issue a tropical storm watch for a portion of the west coast of the Baja peninsula at this time. The motion continues about the same as before, or 010/6 kt. There is little change to the track forecast or reasoning. Simon is moving around the northwestern periphery of a mid-level high pressure area. An approaching shortwave trough should cause the tropical cyclone or its remnant low to move north-northeastward over the next couple of days. The official track forecast is a blend of the latest GFS and ECMWF predictions, with the former guidance farther north and the latter guidance farther south. 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. Please refer to statements from your local weather office for information on hazards specific to your area. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 25.8N 117.4W 45 KT 50 MPH 12H 07/0600Z 26.8N 117.0W 35 KT 40 MPH 24H 07/1800Z 28.0N 116.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 08/0600Z 29.0N 115.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 08/1800Z 30.2N 114.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 09/1800Z 32.0N 112.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 96H 10/1800Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm SIMON Forecast Discussion Number 20

2014-10-06 16:35:45| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON OCT 06 2014 000 WTPZ44 KNHC 061435 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 AM PDT MON OCT 06 2014 Simon's cloud pattern continues to deteriorate...with almost all of the remaining deep convection displaced well to the east and north of the low-level center. Using a blend of Dvorak T-numbers from TAFB and SAB yields a current intensity estimate of 40 kt. The vertical shear over the cyclone is currently near 25 kt, and is forecast to increase to 40-50 kt within the next couple of days. Given the hostile dynamical environment, continued steady weakening is expected. The official forecast shows Simon becoming a remnant low in 36 hours, although this event may well occur sooner than that. The motion is now just east of due north or 010/6 kt. Simon is moving along the northwestern periphery of a low- to mid-level anticyclone. An approaching shortwave trough should cause the cyclone to move north-northeastward, with the remnant low moving across the northern Baja California peninsula and then into extreme northwestern mainland Mexico and the southwestern United States over the next couple of days. The official track forecast follows the dynamical model consensus, TVCE, rather closely. 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. Please refer to statements from your local weather office for information on hazards specific to your area. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 25.1N 117.4W 40 KT 45 MPH 12H 07/0000Z 25.9N 117.2W 35 KT 40 MPH 24H 07/1200Z 27.0N 116.6W 30 KT 35 MPH 36H 08/0000Z 28.1N 116.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 08/1200Z 29.4N 114.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 09/1200Z 32.0N 112.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 96H 10/1200Z...DISSIPATED $$ Forecaster Pasch

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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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