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Hurricane SIMON Forecast Discussion Number 13

2014-10-04 22:47:00| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SAT OCT 04 2014 000 WTPZ44 KNHC 042046 TCDEP4 HURRICANE SIMON DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 PM PDT SAT OCT 04 2014 A NOAA Hurricane Hunter Aircraft, carrying meteorologists from the Meteorological Service of Mexico, reports that Simon has become a major hurricane. The aircraft measured 700 mb flight-level winds of 114 kt, and the Stepped Frequency Microwave Radiometer estimated surface winds of 104 kt. The minimum reported pressure was 950 mb inside a 7 n mi wide eye. Based on this information, the initial intensity is increased to 105 kt. The initial motion is 295/12. Simon is expected to move generally northwestward for the next 24-36 hours or so as is approaches a weakness in the subtropical ridge to its north. After that, the system is expected to turn northward and northeastward. There have been some changes in the track guidance since the last advisory. The ECMWF and Canadian models have shifted to the right and show a faster northward motion, with the ECMWF now calling for landfall on the Baja California peninsula in about four days. The GFS, NAVGEM, and the GFDL continue show Simon moving quickly to the northeast, with the GFS forecasting landfall on the Baja California peninsula in about three days. The new forecast track has not changed much in direction since the last advisory, but it has a faster forward speed. That being said, the new forecast is still slower than the consensus models, and additional adjustments to the speed could be required on later advisories. A combination of microwave imagery and aircraft data suggest that Simon is about to start an eyewall replacement cycle. Some additional strengthening could occur in the next few hours before the eyewall replacement and decreasing sea surface temperatures end intensification. A weakening trend should begin after 12 hours due to the cooler water, and this trend should accelerate after 36 hours as the cyclone encounters increasing shear and a very dry air mass. The new intensity forecast follows the trend of the previous forecast in making Simon a remnant low by the end of the forecast period. An alternative scenario is that Simon could make landfall in Mexico as a weakening tropical cyclone if it moves as fast as the GFS is forecasting. Simon is the eighth major hurricane of the 2014 Eastern North Pacific Hurricane season. This ties the record for major hurricanes set in 1983, 1992, and 1993. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 20.6N 115.0W 105 KT 120 MPH 12H 05/0600Z 21.5N 116.4W 105 KT 120 MPH 24H 05/1800Z 22.7N 117.4W 100 KT 115 MPH 36H 06/0600Z 23.5N 117.6W 85 KT 100 MPH 48H 06/1800Z 24.1N 117.6W 75 KT 85 MPH 72H 07/1800Z 25.5N 117.0W 50 KT 60 MPH 96H 08/1800Z 26.5N 116.0W 35 KT 40 MPH 120H 09/1800Z 27.5N 115.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Hurricane SIMON Forecast Discussion Number 12

2014-10-04 16:49:03| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SAT OCT 04 2014 000 WTPZ44 KNHC 041448 TCDEP4 HURRICANE SIMON DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 AM PDT SAT OCT 04 2014 Infrared satellite imagery indicates that Simon has undergone rapid intensification during the past several hours. A small eye has formed, and the cloud tops surrounding the eye are in the -75C to -85C range. Satellite intensity estimates have increased to 102 kt from TAFB and 90 kt from SAB, and the latest estimated from the CIMSS ADT is 90 kt. Based on these, the initial intensity is increased to 95 kt, and this could be conservative. A NOAA Hurricane Hunter aircraft is scheduled to investigate Simon later today. The initial motion is now 295/11. Simon is expected to move west-northwest to northwestward for the next 36 hours or so as is approaches a weakness in the subtropical ridge to its north. After that, the system is expected to turn northward and northeastward, although there remains significant spread in the track guidance on when and how fast this will occur. The GFS, GFS ensemble mean, NAVGEM, and the GFDL show Simon moving quickly to the northeast, eventually making landfall on the Baja California peninsula and in northwestern Mexico. The ECMWF, UKMET, and CMC models show the turn occurring later and farther west, and these models forecast the cyclone to dissipate over water west of the Baja California peninsula. The forecast track continues to compromise between these two extremes in showing a slow northeastward motion after recurvature. The new forecast track is similar to the previous track and is slower than the model consensus. How long the current rapid intensification will continue is uncertain, as Simon is now moving over decreasing sea surface temperatures. The new intensity forecast follows the guidance trend of showing 12 hours more strengthening. Simon is now forecast to become a major hurricane, and it would not be a surprise if it reached a higher peak intensity than currently forecast. After 12 hours, cooler waters under the forecast track should result in a weakening trend, and this should become more pronounced after 48 hours due to increasing shear. The new intensity forecast shows rapid weakening after 48 hours, with Simon expected to become a remnant low by the end of the forecast period. It should be noted that, if Simon follows the GFS forecast track, it would likely weaken more slowly than currently forecast since it would stay over warmer water and encounters less shear. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 20.2N 113.8W 95 KT 110 MPH 12H 05/0000Z 21.0N 115.3W 105 KT 120 MPH 24H 05/1200Z 22.2N 116.8W 100 KT 115 MPH 36H 06/0000Z 23.1N 117.4W 90 KT 105 MPH 48H 06/1200Z 23.7N 117.6W 80 KT 90 MPH 72H 07/1200Z 24.5N 117.5W 55 KT 65 MPH 96H 08/1200Z 25.5N 117.0W 35 KT 40 MPH 120H 09/1200Z 26.5N 116.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Hurricane SIMON Forecast Discussion Number 11

2014-10-04 10:56:34| National Hurricane Center (East Pacific)

Issued at 200 AM PDT SAT OCT 04 2014 000 WTPZ44 KNHC 040856 TCDEP4 HURRICANE SIMON DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 AM PDT SAT OCT 04 2014 Microwave satellite imagery between 0000 UTC and 0500 UTC indicate that the inner-core convection had been unable to consolidate around the center and maintain a closed eye feature. A 0442 UTC AMSU overpass revealed that the eye of Simon was open in the northwest quadrant. Since that time, however, infrared satellite imagery indicates that a warm spot has developed near the center of a more symmetrical and growing CDO feature, suggesting that Simon might finally be getting more vertically coherent. The initial intensity has been increased to 75 kt based on a Dvorak intensity estimate of T4.5/77 kt from TAFB and the recent appearance of a warm spot in the CDO cloud canopy. The initial motion is 290/10 kt, which is based on several microwave satellite positions. There is basically no significant change to the previous track forecast or reasoning. The 00 UTC model guidance shows less divergence than previous runs, especially through 36 hours. After that time, the models show some noticeable difference on when and where Simon is expected to gradually recurve to the northeast when the cyclone nears the subtropical ridge axis that is situated along 23N-24N latitude. The GFS, GFS-ensemble mean, and HWRF models show a sharper and earlier turn to the northeast by about 48 hours due to a weaker ridge, whereas the ECMWF, UKMET, GFDL and NAVGEM models have Simon moving farther west and making a wider and slower turn. Given the high amplitude nature of the large mid-latitude ridge over the western U.S. and eastern Pacific and the deepening trough over the eastern United States, which should help to sustain the current steering flow pattern, the official forecast leans more toward the farther west and slower recurvature model solutions. The NHC forecast track is similar to but a little to the west of the previous forecast track and the consensus model TVCN. The global models indicate that the current impressive outflow and low vertical wind shear patterns surrounding Simon are expected to persist for at least the next 36 hours or so. However, the most significant strengthening, possibly even rapid intensification, is most likely to occur during the next 24 hours while the hurricane remains over sea-surface temperatures of 27-28C and where the depth of the warm water is sufficient to prevent any significant cold upwelling beneath Simon. By 36 hours, passage over cooler SSTs should induce gradual weakening, followed by more rapid weakening on Days 4 and 5 when southwesterly vertical wind shear is expected to increase to 25-40 kt. Simon is forecast to become a remnant low by 120 hours, but this could occur sooner if the cyclone moves farther west than the official forecast track is indicating, which would bring the cyclone over colder water. A NOAA Hurricane Hunter aircraft is scheduled to conduct a research flight into Simon around 1800 UTC today, at which time a better estimate of the strength of the hurricane will be obtained. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 19.5N 112.7W 75 KT 85 MPH 12H 04/1800Z 20.2N 114.4W 85 KT 100 MPH 24H 05/0600Z 21.4N 116.2W 95 KT 110 MPH 36H 05/1800Z 22.3N 117.2W 80 KT 90 MPH 48H 06/0600Z 23.3N 117.6W 70 KT 80 MPH 72H 07/0600Z 24.4N 117.4W 55 KT 65 MPH 96H 08/0600Z 25.2N 117.0W 35 KT 40 MPH 120H 09/0600Z 26.3N 116.1W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Hurricane SIMON Forecast Discussion Number 10

2014-10-04 04:41:33| National Hurricane Center (East Pacific)

Issued at 800 PM PDT FRI OCT 03 2014 000 WTPZ44 KNHC 040241 TCDEP4 HURRICANE SIMON DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 PM PDT FRI OCT 03 2014 Satellite estimates from TAFB, SAB and University of Wisconsin CIMSS indicate that Simon has reached hurricane intensity with 65 kt. Simon is the 13th hurricane of the quite active eastern North Pacific hurricane season of 2014, and another cyclone moving very near or over Socorro Island, Mexico. Hourly observations from that island provided by the Mexican Navy have been very useful in determining the structure of Simon. The cloud pattern is better organized tonight with a small but well- defined inner core as indicated by the convective ring displayed in several microwave overpasses during the past several hours. Simon has the opportunity to strengthen a little more during the next 24 hours as it continues to move over a pool of 29.5 degree Celsius water and extremely low shear. After 36 hours, the circulation of Simon will begin to weaken as it moves over cooler waters and into a more stable environment. The NHC intensity forecast follows the trend of the guidance which suggests Simon reaching its peak intensity in a day or so. The best estimate of the initial motion is toward the west-northwest or 285 degrees at 10 kt. However, Simon is reaching the southwestern edge of the high pressure ridge centered over Mexico, and approaching a large mid-level trough over the Central Pacific. This pattern calls for a gradual turn toward the northwest and north during the next 3 days as indicated in the official forecast. Beyond 3 days, the steering pattern becomes more complex, and the cyclone either recurves to the northeast as suggested by the GFS or begins to meander as forecast by the ECMWF. Since Simon is expected to be a weaker storm by the end of the forecast period, it will likely move little while embedded within the much lighter low-level flow. The last portion of the forecast is highly uncertain. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 19.2N 111.6W 65 KT 75 MPH 12H 04/1200Z 19.9N 113.3W 75 KT 85 MPH 24H 05/0000Z 20.8N 115.3W 85 KT 100 MPH 36H 05/1200Z 21.8N 116.6W 75 KT 85 MPH 48H 06/0000Z 22.5N 117.0W 65 KT 75 MPH 72H 07/0000Z 23.9N 116.9W 50 KT 60 MPH 96H 08/0000Z 25.0N 116.2W 40 KT 45 MPH 120H 09/0000Z 26.0N 115.5W 30 KT 35 MPH $$ Forecaster Avila

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Tropical Storm SIMON Forecast Discussion Number 9

2014-10-03 22:41:32| National Hurricane Center (East Pacific)

Issued at 200 PM PDT FRI OCT 03 2014 000 WTPZ44 KNHC 032041 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 PM PDT FRI OCT 03 2014 Recent visible imagery shows that Simon is getting better organized, with the inner core convection now wrapping around the center. In addition, a recent TRMM overpass shows a well-defined low-level circulation center, and a recent ASCAT overpass shows a few vectors of 50-55 kt. Satellite intensity estimates from TAFB and SAB are 55 kt, and that will be the initial intensity. The initial motion is 285/8. Simon should move generally west- northwestward for the next 24-36 hours as it is steered by the subtropical ridge to the north and northeast. After that time, the track guidance remains very divergent. The GFS, GFS ensemble mean, and GFDL forecast Simon to recurve through a break in the ridge near 116W-117W and move inland over the Baja California peninsula and northwestern Mexico. The GFS has shifted somewhat westward since the last advisory, but this did not change its forecast scenario. The ECMWF, NAVGEM, and Canadian models show Simon moving farther west, with a northward turn delayed until the cyclone is near 120W. The ECMWF and Canadian subsequently show Simon dissipating over water. Overall, the guidance envelope has shifted a little to the west at 48-120 hours since the last advisory, and the official forecast does as well. The new forecast lies between the TVCE consensus and the Florida State Superensemble from 48-120 hours, but is notably slower than both of those models. Simon will be moving over warmer water with SSTs near 28-29C while the deep-layer vertical shear is expected to be light. This should allow continued strengthening until the cyclone encounters cooler waters in about 36 hours. The new intensity forecast has been increased over the previous forecast from 12-96 hours based on current trends and the latest SHIPS model guidance. There remain two major sources of uncertainty in the intensity forecast. The first is that rapid intensification could occur during the next 24 hours or so. Second, how much cool water Simon will encounter is dependent on the track. The GFS/GFS Ensemble Mean/GFDL track would keep the storm over relatively warm water, while the ECMWF/NAVGEM/ Canadian track would take it over much cooler water. The ASCAT data shows that Simon remains a very small cyclone in terms of size, with tropical-storm force winds extending no more than 40 n mi from the center. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 18.8N 110.6W 55 KT 65 MPH 12H 04/0600Z 19.2N 112.2W 65 KT 75 MPH 24H 04/1800Z 20.0N 114.3W 75 KT 85 MPH 36H 05/0600Z 20.9N 115.6W 80 KT 90 MPH 48H 05/1800Z 21.9N 116.4W 80 KT 90 MPH 72H 06/1800Z 23.5N 116.5W 65 KT 75 MPH 96H 07/1800Z 24.5N 116.0W 50 KT 60 MPH 120H 08/1800Z 25.5N 115.5W 35 KT 40 MPH $$ Forecaster Beven

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