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Tropical Storm Leslie Forecast Discussion Number 40

2018-10-06 10:49:28| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Oct 06 2018 000 WTNT43 KNHC 060849 TCDAT3 Tropical Storm Leslie Discussion Number 40 NWS National Hurricane Center Miami FL AL132018 500 AM AST Sat Oct 06 2018 Leslie is producing a cluster of deep convection near its center of circulation and a far-reaching band that curls around the eastern side of the expansive circulation. The maximum winds are still estimated to be 50 kt based on last evening's ASCAT pass. Leslie's future intensity will largely be limited by a less-than-ideal thermodynamic environment, with the center moving over water temperatures of 24-25 degrees Celsius within its own cold wake during the next 48 hours. Some weakening is anticipated during that period, and the NHC forecast follows the intensity consensus and HCCA guidance. After 48 hours, some restrengthening is possible when Leslie reaches some warmer waters, although increasing westerly shear is likely to temper the amount of intensification. Leslie's current motion is northeastward, or 045/7 kt. The cyclone is becoming increasingly embedded within the mid-latitude westerlies, and these winds, with the assistance of a couple of shortwave troughs, are expected to push Leslie toward the east and southeast throughout the forecast period. The one notable model anomaly is the ECMWF, which shows Leslie becoming more separated from the mid-latitude flow and moving more slowly than shown in the other models on days 3 through 5. Even with that model being an outlier, the rest of the guidance has sped up a bit, pulling the consensus aids eastward. This resulted in the new NHC track forecast being a little faster than the previous one on days 4 and 5. Large swells generated by Leslie are expected to continue during the next few days across the eastern coast of the United States, Bermuda, the Bahamas, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 37.2N 56.4W 50 KT 60 MPH 12H 06/1800Z 37.3N 55.0W 50 KT 60 MPH 24H 07/0600Z 37.1N 52.6W 50 KT 60 MPH 36H 07/1800Z 36.5N 50.2W 45 KT 50 MPH 48H 08/0600Z 35.7N 47.8W 40 KT 45 MPH 72H 09/0600Z 33.4N 42.6W 45 KT 50 MPH 96H 10/0600Z 30.5N 37.5W 50 KT 60 MPH 120H 11/0600Z 28.5N 32.5W 50 KT 60 MPH $$ Forecaster Berg

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Hurricane Sergio Forecast Discussion Number 28

2018-10-06 10:45:58| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sat Oct 06 2018 000 WTPZ41 KNHC 060845 TCDEP1 Hurricane Sergio Discussion Number 28 NWS National Hurricane Center Miami FL EP212018 200 AM PDT Sat Oct 06 2018 Sergio has changed little in structure since the last advisory. It still has a 25-30 n mi wide eye surrounded by cold convective tops, and with not much change in intensity estimates, the estimated maximum winds remain 110 kt. Sergio's intensity is not likely to change much during the next day or two, although some slight weakening is possible as the hurricane's speed slows down and it upwells some colder water from below, or due to possible internal structural changes. More definitive weakening is anticipated by days 4 and 5 due to an increase in westerly and southwesterly shear and the hurricane reaching colder waters. The NHC intensity forecast remains close to a blend of the ICON consensus and the HCCA model. However, the statistical-dynamical models remain a bit higher, and it is possible that Sergio won't lose quite as much punch during the next several days as is indicated by the official forecast. Sergio continues to dive southwestward with an initial motion of 235/7 kt. A shortwave trough swinging across the Baja California peninsula will bypass Sergio during the day, leaving a weakness in the ridge that will allow the hurricane to begin making a sharp northward and then northeastward turn during the next 24-72 hours. Another shortwave trough forecast to dig southward off the California coast will then cause Sergio to accelerate northeastward on days 4 and 5. Notable changes in this forecast update include a slightly wider turn from 24-72 hours, and more spread in the model speeds once Sergio accelerates toward the Baja California peninsula. As is usually the case in these scenarios, the ECMWF is much slower than the other models, and because of that, the new NHC forecast is a bit slower than the previous one, especially on day 5. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 14.9N 123.5W 110 KT 125 MPH 12H 06/1800Z 14.6N 124.4W 105 KT 120 MPH 24H 07/0600Z 14.4N 125.6W 100 KT 115 MPH 36H 07/1800Z 14.7N 126.5W 95 KT 110 MPH 48H 08/0600Z 15.2N 127.0W 90 KT 105 MPH 72H 09/0600Z 16.9N 126.1W 80 KT 90 MPH 96H 10/0600Z 19.0N 123.0W 65 KT 75 MPH 120H 11/0600Z 23.0N 118.0W 55 KT 65 MPH $$ Forecaster Berg

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Hurricane Sergio Forecast Discussion Number 27

2018-10-06 04:32:56| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Fri Oct 05 2018 000 WTPZ41 KNHC 060232 TCDEP1 Hurricane Sergio Discussion Number 27 NWS National Hurricane Center Miami FL EP212018 800 PM PDT Fri Oct 05 2018 Sergio has maintained a 25-30-nmi wide eye this evening, and a ring of cold cloud tops has cooled around the well-defined eye. Satellite intensity estimates range from T5.5/102 kt from TAFB and SAB to T5.9/122 kt from ADT and a T6.0/115 kt NHC objective T-number, so the intensity has been bumped up to 110 kt for this advisory. Upper-level outflow and the overall convective pattern have both improved since the previous advisory while Sergio has lost latitude and moved over warmer waters. The motion is now southwestward, or 235/06 kt. Sergio's recent southwestward motion is forecast to be short lived, with a return to a west-southwestward to westward motion expected within the next 12 hours. The deep-layer ridge to the north of Sergio is forecast to become more narrow due to a passing shortwave trough, but it is basically expected to remain intact. This feature will steer the hurricane slowly westward through Sunday. By Monday, however, a stronger trough is forecast by the global models to drop southward off the coasts of California and Baja California, causing a significant weakening and erosion of the western portion of the ridge. This is expected to result in Sergio turning slowly northeastward on Monday, and accelerate on days 4 and 5. The new NHC forecast track is similar to the previous advisory track, and lies close to consensus models TVCE and NOAA-HCCA. Other than very brief intrusions of dry mid-level air and possible upwelling beneath the hurricane due to its slow forward speed, there do not appear to be any other negative factors that would significantly disrupt Sergio's intensity for the next 36-48 hours. By 72 hours and beyond, however, increasing southwesterly vertical wind shear is expected to induce a steady weakening trend after the cyclone begins accelerating toward the northeast, and on days 4 and 5 passing over the cold wake left behind by former Hurricane Rosa. The new official intensity forecast is similar to the previous one, and is near an average of the NOAA-HCCA and IVCN consensus models. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 15.3N 122.7W 110 KT 125 MPH 12H 06/1200Z 15.0N 123.6W 110 KT 125 MPH 24H 07/0000Z 14.7N 124.8W 105 KT 120 MPH 36H 07/1200Z 14.8N 125.8W 100 KT 115 MPH 48H 08/0000Z 15.4N 126.5W 95 KT 110 MPH 72H 09/0000Z 17.1N 126.0W 85 KT 100 MPH 96H 10/0000Z 19.4N 122.7W 70 KT 80 MPH 120H 11/0000Z 23.0N 118.0W 60 KT 70 MPH $$ Forecaster Stewart

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Tropical Storm Leslie Forecast Discussion Number 39

2018-10-06 04:32:25| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Oct 05 2018 000 WTNT43 KNHC 060232 TCDAT3 Tropical Storm Leslie Discussion Number 39 NWS National Hurricane Center Miami FL AL132018 1100 PM AST Fri Oct 05 2018 Leslie's cloud pattern consists of a small ring of shallow to moderate convection embedded within a large and vigorous circulation. Dvorak classifications allow me to keep the same intensity, and in fact, ASCAT data just came in with a few 50-kt wind vectors. So the initial intensity remains at 50 kt in this advisory. Leslie will not encounter any hostile shear, but the cyclone will move over a few patches of warm and cool waters. The guidance shows some minor fluctuations in the cyclone intensity, most likely due to the aforementioned SST variations along the track, and this is reflected in the NHC forecast. Leslie is moving toward the east-northeast or 075 degrees at 6 kt. The cyclone is already embedded in the mid-latitude westerly flow, which is being modulated by passing shortwaves. This flow pattern is expected to persist and should steer Leslie eastward and east-southeastward through the next 5 days. Although the track guidance is not as clustered as in previous days, most of the models agree with the eastward motion of the cyclone, but vary in speed. It appears that stubborn Leslie will be with us for several more days. Large swells generated by Leslie are expected to continue during the next few days across the eastern coast of the United States, Bermuda, the Bahamas, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 36.6N 57.2W 50 KT 60 MPH 12H 06/1200Z 37.0N 56.0W 50 KT 60 MPH 24H 07/0000Z 37.0N 54.0W 50 KT 60 MPH 36H 07/1200Z 36.5N 51.7W 50 KT 60 MPH 48H 08/0000Z 36.0N 49.5W 45 KT 50 MPH 72H 09/0000Z 34.0N 45.0W 45 KT 50 MPH 96H 10/0000Z 31.0N 41.0W 50 KT 60 MPH 120H 11/0000Z 29.0N 38.0W 55 KT 65 MPH $$ Forecaster Avila

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Tropical Storm Leslie Forecast Discussion Number 38

2018-10-05 22:40:51| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Oct 05 2018 000 WTNT43 KNHC 052040 TCDAT3 Tropical Storm Leslie Discussion Number 38 NWS National Hurricane Center Miami FL AL132018 500 PM AST Fri Oct 05 2018 Leslie is currently maintaining a small central convective feature and an outer convective band in the southeastern semicircle. The various satellite intensity estimates have decreased a little, so the initial intensity is nudged downward to 50 kt. This is still a little above the estimates from TAFB, SAB, and the CIMSS satellite consensus. While no data was available from the inner core, scatterometer overpasses this morning suggests that Leslie has changed little in size since last night. Leslie has now slowed its forward motion and is starting to turn more eastward, with an initial motion of 030/3. A turn to the east is expected during the next 24 h, followed by a turn toward the east-southeast by 36 h as Leslie encounters the southern edge of the mid-latitude westerlies. A general motion toward the east-southeast or southeast should then continue for the remainder of the forecast period. The latest guidance again shifted southward, and the new forecast track, which is in best agreement with the TVCN consensus model, is shifted to the south of the previous track The forecast track again takes Leslie over cooler waters around day 2, into slightly stronger shear around day 3, and over warmer water with decreasing shear around days 4-5. However, the structure of Leslie is not currently conducive for rapid changes in intensity either up or down. Thus, the intensity forecast, which has only minor tweaks from the previous forecast, follows the trend of the previous forecast and the guidance in showing gradual weakening near 48 h, followed by slight intensification near 96-120 h. Large swells generated by Leslie are expected to continue during the next few days across the eastern coast of the United States, Bermuda, the Bahamas, the Greater and Lesser Antilles, and Atlantic Canada. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 36.2N 58.1W 50 KT 60 MPH 12H 06/0600Z 36.7N 57.5W 50 KT 60 MPH 24H 06/1800Z 36.7N 55.8W 50 KT 60 MPH 36H 07/0600Z 36.4N 53.8W 50 KT 60 MPH 48H 07/1800Z 35.8N 51.7W 45 KT 50 MPH 72H 08/1800Z 34.0N 48.0W 45 KT 50 MPH 96H 09/1800Z 31.5N 44.5W 50 KT 60 MPH 120H 10/1800Z 30.0N 42.0W 55 KT 65 MPH $$ Forecaster Beven

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