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Tropical Storm Leslie Forecast Discussion Number 15
2018-09-30 04:43:25| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Sep 29 2018 200 WTNT43 KNHC 300243 TCDAT3 Tropical Storm Leslie Discussion Number 15 NWS National Hurricane Center Miami FL AL132018 1100 PM AST Sat Sep 29 2018 The structure of Leslie consists of a large, broken outer band wrapped around the eastern semicircle of the cyclone, with little convection west of the center. ASCAT data recently showed 40-45 kt within that band, so the maximum winds will stay at 45 kt. The storm should gradually move over somewhat warmer waters within a lighter shear environment during the next few days. Thus gradual intensification is shown, similar to the model consensus. The only notable change to the previous forecast is to move up the peak intensity close to Leslie's southernmost position before it stalls. It would seem that after that time, the relatively large system would be moving close to its previous track over its self-generated cooler upwelled waters, and weaken somewhat at long range. Leslie continues to move southwestward, and its initial motion is 235/5 kt. This storm should move slowly to the southwest through Sunday, then creep southward by late Monday due to steering partially by northerly flow from a distant ridge over the western Atlantic and a nearby large mid- to upper-level trough. Eventually, a new ridge rebuilds over the east-central Atlantic east of Leslie, which causes the cyclone to move to the north at a faster pace by day 5. As you could imagine in such a complex pattern, the models aren't in good agreement on how quickly the storm ejects, and this is a pretty uncertain forecast at long range. Until some forecast scenarios become clear, the forecast will stay close to the corrected-consensus aids, resulting in mostly cosmetic changes to the last forecast. Large swells generated by Leslie when it was a strong extratropical low will affect Bermuda, the east coast of the United States, and most of the Greater and Lesser Antilles through at least the weekend. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 33.9N 52.0W 45 KT 50 MPH 12H 30/1200Z 33.4N 52.8W 45 KT 50 MPH 24H 01/0000Z 33.0N 53.4W 50 KT 60 MPH 36H 01/1200Z 32.6N 53.9W 50 KT 60 MPH 48H 02/0000Z 32.2N 54.2W 55 KT 65 MPH 72H 03/0000Z 31.0N 54.5W 65 KT 75 MPH 96H 04/0000Z 31.7N 54.2W 60 KT 70 MPH 120H 05/0000Z 34.5N 53.5W 60 KT 70 MPH $$ Forecaster Blake
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Tropical Storm Sergio Forecast Discussion Number 3
2018-09-30 04:40:25| National Hurricane Center (East Pacific)
Issued at 1000 PM CDT Sat Sep 29 2018 273 WTPZ41 KNHC 300240 TCDEP1 Tropical Storm Sergio Discussion Number 3 NWS National Hurricane Center Miami FL EP212018 1000 PM CDT Sat Sep 29 2018 Satellite images indicate that Sergio has become better organized during the past several hours with more concentrated convection near the center. Intensity estimates are slightly higher than the past advisory, so the initial wind speed is set to 40 kt, closest to the CIMSS SATCON. The storm should be in a low-shear, warm-water, and high-moisture environment for the next 2 or 3 days. While there are no signs of an inner core forming yet, that usually doesn't stop steady intensification, and rapid strengthening is a distinct possibility in a day or two. Thus the intensity forecast is raised from the previous one and is close to the consensus. Although there are a number of reliable models showing a higher peak intensity, an uncertain environment at long range leads me to a more conservative forecast. It would not be surprising at all if my prediction ended up being too low, given the intense nature of this eastern Pacific hurricane season. The initial motion is close to the prevous one, 275/9. Sergio should be steered generally westward for the next two or three days by the subtropical ridge over Mexico. After that time, the cyclone is forecast to approach a weakness in the ridge caused by a large mid- to upper-level trough over California, and this should lead to a turn toward the northwest. Similar to the previous advisory, the track guidance has shifted slightly south and west, so the official forecast is nudged in that direction at most time periods. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 12.3N 103.3W 40 KT 45 MPH 12H 30/1200Z 12.4N 104.7W 50 KT 60 MPH 24H 01/0000Z 12.3N 106.9W 65 KT 75 MPH 36H 01/1200Z 12.0N 109.1W 75 KT 85 MPH 48H 02/0000Z 11.8N 111.1W 90 KT 105 MPH 72H 03/0000Z 12.9N 114.8W 100 KT 115 MPH 96H 04/0000Z 15.0N 117.8W 100 KT 115 MPH 120H 05/0000Z 17.0N 120.0W 95 KT 110 MPH $$ Forecaster Blake
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Hurricane Rosa Forecast Discussion Number 20
2018-09-30 04:38:56| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Sat Sep 29 2018 688 WTPZ45 KNHC 300238 TCDEP5 Hurricane Rosa Discussion Number 20 NWS National Hurricane Center Miami FL EP202018 800 PM PDT Sat Sep 29 2018 Recent microwave images indicate that Rosa's structure has begun to deteriorate as a result of increasing southerly shear. Despite the cold cloud tops noted in infrared imagery, the hurricane's eyewall is open on the south side, and there is very little convective banding within the southern half of the circulation. The various subjective and objective intensity estimates have either held steady or fallen a bit from six hours ago, and given the microwave signature, the initial intensity is lowered to 85 kt. Rosa is moving northward, or 360 degrees at 10 kt, along the western edge of a subtropical ridge which extends across northern Mexico. The cyclone is forecast to turn north-northeastward and accelerate slightly during the next 48-72 hours as it is steered between the ridge and a large mid- to upper-level trough located off the west coast of the United States. The track guidance is clustered fairly tightly, although the ECMWF is notably slower than the rest of the models, taking a little longer to bring Rosa's center to the Baja California peninsula. The updated NHC track forecast was nudged southeastward beyond 36 hours to account for the latest model guidance, and it shows Rosa reaching the coast in about 48 hours. A 72-hour forecast is provided for continuity, but Rosa's surface circulation is likely to dissipate before that time over northwestern Mexico or southern Arizona, with the mid-level remnants continuing northward across the Desert Southwest and Intermountain West. Rosa is now over waters colder than 26 degrees Celsius, and combined with increasing vertical shear, the cyclone's intensity is expected to decrease quickly, with rapid weakening even a possibility beginning on Sunday. The official forecast follows the sharp weakening trend noted in the guidance, and it's actually slightly above the intensity consensus at a few forecast times. Rosa is likely to devolve into an exposed low-level center with the associated deep convection being sheared off to its north and northeast by the time it is nearing the Baja California coast on Monday. However, it will take some time for the circulation to spin down, and Rosa is still expected to bring tropical-storm-force winds to portions of Baja California in 36-48 hours. Based on the new track and intensity forecast, a Tropical Storm Warning and Watch has been issued for portions of the west and east coast of the Baja California peninsula, respectively. Key Messages: 1. The main hazard expected from Rosa or its remnants is very heavy rainfall in Baja California, northwestern Sonora, and the U.S. Desert Southwest. These rains are expected to produce life-threatening flash flooding and debris flows in the deserts, and landslides in mountainous terrain. For more information about potential rainfall in that area, please see products from the Weather Prediction Center and your local NWS forecast office. 2. Tropical storm conditions are expected over portions of the central and northern Baja California peninsula on Monday, possibly spreading to the northern Gulf of California Monday night. Interests in those locations should monitor the progress of Rosa. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 22.4N 118.9W 85 KT 100 MPH 12H 30/1200Z 23.9N 118.7W 75 KT 85 MPH 24H 01/0000Z 25.7N 117.7W 60 KT 70 MPH 36H 01/1200Z 27.5N 116.5W 45 KT 50 MPH 48H 02/0000Z 29.6N 115.3W 35 KT 40 MPH...OVER BAJA CALIFORNIA 72H 03/0000Z 35.7N 111.4W 20 KT 25 MPH...POST-TROP/INLAND 96H 04/0000Z...DISSIPATED $$ Forecaster Berg
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Tropical Storm Sergio Forecast Discussion Number 2
2018-09-29 22:42:25| National Hurricane Center (East Pacific)
Issued at 400 PM CDT Sat Sep 29 2018 388 WTPZ41 KNHC 292042 TCDEP1 Tropical Storm Sergio Discussion Number 2 NWS National Hurricane Center Miami FL EP212018 400 PM CDT Sat Sep 29 2018 Recent scatterometer data confirms that Sergio is at tropical storm strength, but with a slightly unexpected twist - the maximum winds are in a band about 110 n mi east of the center and there is no inner wind core at this time. The initial intensity remains 35 kt based on the scatterometer data. Sergio currently has good cirrus outflow in all directions, but there is some evidence that northerly upper-level winds below the level of the outflow are causing some light shear. Sergio is expected to be in an environment of light vertical shear and high humidity, and over warm sea surface temperatures for the next 3 days or so, which should result in steady strengthening. The environment is favorable enough for rapid intensification, although the current storm structure does not appear favorable for quick strengthening. The intensity forecast calls for gradual intensification during the first 24-36 h, with a faster rate from 36-72 h as the cyclone becomes better organized. Near the end of the forecast period, the storm may encounter increasing northeasterly shear which could limit intensification, and this is reflected in the forecast. The intensity forecast is in the middle of the guidance envelope and just above the intensity consensus, and the forecast may need to be adjusted upward in subsequent advisories. The wind radii forecast have been adjusted based on the current structure and the latest radii guidance. The initial motion is now 275/10. Sergio should be steered generally westward for the next three days or so by the subtropical ridge over Mexico. After that time, the cyclone should approach a weakness in the ridge caused by a large mid- to upper-level trough over California, and this should lead to a turn toward the northwest. The track guidance remains in good agreement with this scenario, and the new forecast track is similar to, but a little south of, the previous track. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 12.1N 102.8W 35 KT 40 MPH 12H 30/0600Z 12.3N 104.3W 40 KT 45 MPH 24H 30/1800Z 12.3N 106.3W 50 KT 60 MPH 36H 01/0600Z 12.2N 108.3W 60 KT 70 MPH 48H 01/1800Z 12.1N 110.2W 75 KT 85 MPH 72H 02/1800Z 13.0N 114.0W 95 KT 110 MPH 96H 03/1800Z 15.0N 117.5W 95 KT 110 MPH 120H 04/1800Z 16.5N 119.5W 95 KT 110 MPH $$ Forecaster Beven
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Hurricane Rosa Forecast Discussion Number 19
2018-09-29 22:42:25| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Sat Sep 29 2018 389 WTPZ45 KNHC 292042 TCDEP5 Hurricane Rosa Discussion Number 19 NWS National Hurricane Center Miami FL EP202018 200 PM PDT Sat Sep 29 2018 The strengthening trend seen earlier has at least slowed, as Rosa has shown little change in organization since the last advisory. The hurricane continues to have a well-defined 30-40 n mi wide eye inside a central dense overcast with cloud tops as cold as -75C. The various satellite intensity estimates have changed little, so the initial intensity remains 90 kt. The hurricane has good to excellent cirrus outflow in the northeastern semicircle, and the outflow has recently improved in the southwestern semicircle. Rosa is now crossing the 26C isotherm, so additional significant strengthening appears unlikely. After 12 h, the combination of decreasing sea surface temperatures and increasing shear should cause steady to rapid weakening, and the intensity forecast continues to call for the cyclone to weaken below hurricane strength before the center reaches the Baja California peninsula in just over 48 h. After landfall, the surface circulation is forecast to dissipate near the 72-h point in agreement with all of the dynamical models. However, the mid-level circulation and the associated rainfall will continue moving across the southwestern United States after the surface circulation dissipates. The initial motion is 350/10. During the forecast period, the hurricane will recurve into the westerlies between a deep-layer ridge over northern Mexico and a large mid- to upper-level trough over California and the adjacent Pacific. This should result in a continued northward motion through tonight, followed by a turn toward the north-northeast on Sunday. The new forecast track is a little to the left of the previous track for the first 12 h, but otherwise is changed little from the previous track. On the forecast track, the center of Rosa or its remnants will move near or over the central and northern portions the Baja California peninsula on Monday and Monday night, and then move into the southwestern United States on Tuesday. Key Messages: 1. The main hazard expected from Rosa or its remnants is very heavy rainfall in Baja California, northwestern Mexico, and the Desert Southwest. These rains are expected to produce life-threatening flash flooding and debris flows in the deserts, and landslides in mountainous terrain. For more information about potential rainfall in that area, please see products from the Weather Prediction Center and your local NWS forecast office. 2. Rosa could also bring tropical storm conditions to portions of the central and northern Baja California peninsula starting on Monday. Interests in those locations should monitor the progress of Rosa. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 21.4N 118.7W 90 KT 105 MPH 12H 30/0600Z 22.9N 118.9W 85 KT 100 MPH 24H 30/1800Z 24.8N 118.3W 70 KT 80 MPH 36H 01/0600Z 26.7N 117.1W 55 KT 65 MPH 48H 01/1800Z 28.8N 116.0W 40 KT 45 MPH 72H 02/1800Z 34.5N 113.0W 20 KT 25 MPH...POST-TROP/INLAND 96H 03/1800Z...DISSIPATED $$ Forecaster Beven
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