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Tropical Storm SIMON Forecast Discussion Number 7

2014-10-03 10:57:54| National Hurricane Center (East Pacific)

Issued at 200 AM PDT FRI OCT 03 2014 000 WTPZ44 KNHC 030857 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 AM PDT FRI OCT 03 2014 Microwave satellite images early this morning indicate that the inner-core region of Simon is not particularly well organized. A low-level eye feature has been intermittent since about 0000 UTC, but the most recent images do not show the eye feature any longer. Subjective and objective satellite intensity estimates suggest that Simon has strengthened to 55-60 kt based on a CDO feature. However, two ASCAT overpasses at 0412 UTC and 0504 UTC only indicated surface winds of 39 kt and 41 kt, respectively. Even allowing for some undersampling due to the compact size of the cyclone likely only yields 45-50 kt. Owing to the lack of persistent central features, the initial intensity is being held at 45 kt for this advisory. The initial motion is an uncertain 280/06 kt and is based primarily on microwave satellite fixes. There remains high confidence that Simon will continue to move westward to west-northwestward for the next 2-3 days as the cyclone navigates around the western periphery of a strong deep-layer ridge located north of the cyclone. After that time, however, the model guidance diverges quite significantly. The overwhelming majority of the guidance recurves Simon toward the north by Day 4 and toward the northeast by Day 5. However, the very reliable ECMWF model takes Simon farther west through Day 5 and does not recurve the cyclone until after this forecast period. Owing to the significant differences in the various model solutions, and out of respect for the ECMWF model, and given that mid-level northwesterly flow patterns are not conducive for recurvature scenarios, the official forecast was only nudged a little to the west of the previous forecast track. Simon will be moving over warmer water with SSTs near 28-29C during the next 24-36 hours while the deep-layer vertical shear is light. However, modest easterly mid-level shear that has been undercutting the otherwise impressive outflow pattern may continue to occasionally disrupt the inner core convection before Simon reaches cooler water and a drier, more stable airmass by Days 4 and 5. As a result, only slow steady strengthening is forecast, which is similar to the SHIPS intensity model and the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 18.3N 108.9W 45 KT 50 MPH 12H 03/1800Z 18.7N 110.3W 55 KT 65 MPH 24H 04/0600Z 19.3N 112.2W 65 KT 75 MPH 36H 04/1800Z 20.0N 114.1W 75 KT 85 MPH 48H 05/0600Z 21.0N 115.8W 75 KT 85 MPH 72H 06/0600Z 22.5N 116.5W 60 KT 70 MPH 96H 07/0600Z 24.0N 116.0W 50 KT 60 MPH 120H 08/0600Z 25.0N 115.5W 35 KT 40 MPH $$ Forecaster Stewart

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Tropical Storm SIMON Forecast Discussion Number 6

2014-10-03 04:36:23| National Hurricane Center (East Pacific)

Issued at 800 PM PDT THU OCT 02 2014 000 WTPZ44 KNHC 030236 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 PM PDT THU OCT 02 2014 A series of microwave overpasses during the past few hours confirmed that Simon is a little south and east of previous estimates, and that the cyclone is now moving westward or 270 degrees at 4 kt. Although the cloud pattern is gradually becoming better organized with more symmetric convection and better-defined outflow, Dvorak estimates from TAFB and SAB indicate that the winds are still 45 kt. The CIMSS-ADT indicate that Simon could be a little stronger. Simon is forecast to move soon over a pool of even warmer water and the shear is light. This should result in strengthening, and the NHC forecast calls for Simon to become a hurricane in about 24 hours. In fact, rapid intensification is not out of the question since the SHIPS-RI index has increased again tonight. After 3 days, the circulation of the cyclone will begin to feel the influence of cooler waters and a stable environment, and gradual weakening should commence. There is high confidence that Simon will gradually turn to the northwest with an increase in forward speed during the next 3 days while the cyclone is located on the southwestern side of the high pressure system over Mexico. Most of the track guidance agree with this scenario. After that time, the confidence in the track forecast is quite low since the GFS together with its dependent models recurve the cyclone toward the Baja California peninsula. On the contrary, the ECMWF keeps Simon moving westward over open waters. The NHC forecast is in the middle of these two extremes, and for now keeps Simon drifting northward by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 18.1N 108.2W 45 KT 50 MPH 12H 03/1200Z 18.3N 109.8W 55 KT 65 MPH 24H 04/0000Z 18.9N 111.5W 65 KT 75 MPH 36H 04/1200Z 19.6N 113.3W 70 KT 80 MPH 48H 05/0000Z 20.7N 114.8W 75 KT 85 MPH 72H 06/0000Z 22.5N 115.6W 70 KT 80 MPH 96H 07/0000Z 24.0N 115.5W 60 KT 70 MPH 120H 08/0000Z 24.5N 115.5W 40 KT 45 MPH $$ Forecaster Avila

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Tropical Storm SIMON Forecast Discussion Number 5

2014-10-02 23:00:20| National Hurricane Center (East Pacific)

Issued at 200 PM PDT THU OCT 02 2014 000 WTPZ44 KNHC 022100 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 PM PDT THU OCT 02 2014 The center of Simon has either re-formed or has made a large wobble during the past few hours, as a TRMM overpass at 1827 UTC suggests the center is well southwest of the position seen in earlier SSM/IS overpasses. This requires a southward adjustment of the initial position. The new advisory position is still north of the TRMM position, and an additional adjustment may be required later if no subsequent northward wobble occurs. The initial intensity is increased to 45 kt based on satellite intensity estimates from TAFB and SAB, along with CIMSS ADT and CIRA AMSU estimates. The initial motion is a rather uncertain 280/8. For the next day or so, mid-level ridging to the north and northeast of the cyclone should steer Simon generally westward to west-northwestward. From 24-72 hours, the cyclone should turn more northward as it approaches the western end of the ridge. The guidance continues to show significant divergence after that. The GFS, GFDL, and HWRF, show a northeastward turn between 72-120 hours and bring Simon close to Baja California in 96-120 hours. On the other hand, the the ECMWF and UKMET show a generally northwestward motion that keeps the center well away from land. The track forecast compromises between these extremes by showing a slow northward motion by 120 hours. The new forecast is shifted to the south and west of the previous forecast based on current trends, and it is in best overall agreement with the Florida State Superensemble. Simon is forecast to remain in a light vertical wind shear environment and over sea surface temperatures of 28-29C for the next 48 hours, which should allow at least steady strengthening. After that, movement over cooler water should cause weakening. The new intensity forecast is increased over the previous forecast in best overall agreement with the SHIPS model, and it lies near the upper edge of the intensity guidance. An alternative forecast scenario is that rapid intensification begins in the next 12-24 hours, with Simon becoming significantly stronger than forecast. This scenario is supported by above average probabilities in the Rapid Intensification Index of the SHIPS model, and by the TRMM data, which suggests Simon is developing a small inner core. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 18.3N 108.0W 45 KT 50 MPH 12H 03/0600Z 18.6N 109.2W 50 KT 60 MPH 24H 03/1800Z 19.0N 111.0W 60 KT 70 MPH 36H 04/0600Z 19.7N 112.6W 70 KT 80 MPH 48H 04/1800Z 20.7N 114.1W 75 KT 85 MPH 72H 05/1800Z 22.5N 115.5W 70 KT 80 MPH 96H 06/1800Z 24.0N 116.0W 60 KT 70 MPH 120H 07/1800Z 25.0N 116.0W 45 KT 50 MPH $$ Forecaster Beven

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Tropical Storm SIMON Forecast Discussion Number 4

2014-10-02 16:45:21| National Hurricane Center (East Pacific)

Issued at 800 AM PDT THU OCT 02 2014 000 WTPZ44 KNHC 021445 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 800 AM PDT THU OCT 02 2014 First-light visible imagery shows that Simon is gradually becoming better organized. The center is under a ragged central dense overcast, and outer bands are occurring in all quadrants except the north. Satellite intensity estimates from TAFB and SAB are 35 kt, while recent AMSU and SATCON estimates from CIMSS are 35-40 kt. The initial intensity remains 35 kt, but this could be a little conservative. The initial motion is 295/9, and this general motion is expected to continue for the next 2 days or so while the storm is steered by mid-level ridging to its north and northeast. The model guidance is in fair agreement during that time period, and the NHC track forecast remains near the middle of the guidance envelope. The guidance continues to show significant divergence after 48 hours. The GFS, GFDL, and HWRF, show a northeastward turn between 72-120 hours, while the the ECMWF and UKMET show a generally northward motion. In addition, the NAVGEM shows a west-northwestward motion through the entire forecast period. The track forecast compromises between these extremes by showing a slow northward motion by 120 hours. Overall, the new forecast is similar to, but faster than, the previous forecast. However, it is notably slower than the consensus model TVCE from 72-120 hours. Simon is forecast to remain in a light vertical wind shear environment and over sea surface temperatures of 28-29C for the next 48 hours. This should allow at least steady strengthening, and there is an above normal chance for rapid strengthening as shown by the Rapid Intensification Index of the SHIPS model. After 48 hours, the center is expected to move over cooler sea surface temperatures and into an area of westerly shear. These conditions should cause a weakening trend, albeit at a slower rate than seen during Rachel a few days ago. The new intensity forecast is increased above that of the previous forecast and is in best overall agreement with the SHIPS model. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 18.4N 107.1W 35 KT 40 MPH 12H 03/0000Z 18.9N 108.4W 40 KT 45 MPH 24H 03/1200Z 19.3N 110.3W 50 KT 60 MPH 36H 04/0000Z 19.8N 112.0W 60 KT 70 MPH 48H 04/1200Z 20.4N 113.5W 70 KT 80 MPH 72H 05/1200Z 22.5N 115.5W 70 KT 80 MPH 96H 06/1200Z 24.0N 115.5W 60 KT 70 MPH 120H 07/1200Z 25.0N 115.5W 45 KT 50 MPH $$ Forecaster Beven

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Tropical Storm SIMON Forecast Discussion Number 3

2014-10-02 10:37:18| National Hurricane Center (East Pacific)

Issued at 200 AM PDT THU OCT 02 2014 000 WTPZ44 KNHC 020837 TCDEP4 TROPICAL STORM SIMON DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192014 200 AM PDT THU OCT 02 2014 Satellite images indicate that curved banding features have become better established during the last several hours, and the low-level center is now estimated to be located beneath the deep convection. Dvorak classifications from TAFB, SAB, and the University of Wisconsin-CIMSS all support raising the initial wind speed to 35 kt, making the system Tropical Storm Simon. This is the 18th named storm of the busy 2014 hurricane season in the east Pacific basin. Simon is expected to strengthen during the next few days while the storm remains over warm water and within a fairly low wind shear and moist environment. The combination of an increase in southwesterly shear and cooler water should stop the strengthening trend in about 3 days, and induce a gradual weakening. The NHC intensity forecast is a little above the intensity model consensus, given the expected favorable conditions during the next few days, leaning toward the more aggressive SHIPS model. Simon is moving west-northwestward at about 9 kt, and this general motion is expected to continue for the next 2 to 3 days while the storm is steered by mid-level ridging to its north and northeast. The model guidance is in fair agreement during that time period, and the NHC track forecast lies near the middle of the guidance envelope. The guidance diverges significantly beyond that time period, however, with many of the models showing a turn to the north and then northeast toward large-scale troughing over the U.S. Conversely, the ECMWF shows less interaction with the trough and takes the storm farther west. The NHC track forecast lies on the western side of the guidance envelope at days 4 and 5, similar to the previous forecast, but confidence at the longer range is low at this time. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 18.1N 106.1W 35 KT 40 MPH 12H 02/1800Z 18.5N 107.2W 40 KT 45 MPH 24H 03/0600Z 18.9N 108.9W 50 KT 60 MPH 36H 03/1800Z 19.3N 110.6W 55 KT 65 MPH 48H 04/0600Z 19.9N 112.2W 60 KT 70 MPH 72H 05/0600Z 21.5N 114.7W 60 KT 70 MPH 96H 06/0600Z 23.2N 115.5W 50 KT 60 MPH 120H 07/0600Z 24.0N 115.5W 40 KT 45 MPH $$ Forecaster Cangialosi

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