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Hurricane Sergio Forecast Discussion Number 21

2018-10-04 16:44:40| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Thu Oct 04 2018 543 WTPZ41 KNHC 041444 TCDEP1 Hurricane Sergio Discussion Number 21 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Thu Oct 04 2018 Sergio remains a strong hurricane this morning, with subjective Dvorak estimates range from 5.5 (102 kt) to 6.5 (127 kt). While some slightly drier air has been ingested into the eyewall, cloud top temperatures have cooled recently and Sergio appears poised to once again close off this dry air channel. Based on these data, the initial intensity is held at 120 kt. The intensity forecast is mostly a continuation of the previous advisory, but is slightly lower after 24 hours to reflect a blend of HCCA and other consensus aids. Vertical wind shear from GFS/SHIPS is forecast to remain at or below approximately 10 kt through 48 hours before increasing to above 15 kt by Saturday. The primary limiter on Sergio's intensity appears to be SSTs which will drop off gradually, especially by the end of the forecast. Sergio is continuing to move northwestward around the mid-level ridge which extends into the Pacific off of Mexico. The initial motion is 320/8 kt. Objective track guidance is in fairly good agreement on a gradual turn toward the west tonight and Friday in response to a second ridge which builds in from the west. Guidance remains in decent agreement on Sergio then turning back northeastward by the end of the forecast period as this ridge lifts northward and a highly-amplified mid-level trough digs into western North America. The official track forecast is very similar to the previous advisory through day 4 with a small shift eastward thereafter to reflect a slightly earlier northeast turn in the guidance. This track philosophy is supported by essentially all of the ECMWF/GFS ensemble members as well. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 15.0N 119.3W 120 KT 140 MPH 12H 05/0000Z 15.6N 120.2W 120 KT 140 MPH 24H 05/1200Z 16.0N 121.5W 110 KT 125 MPH 36H 06/0000Z 16.0N 122.8W 100 KT 115 MPH 48H 06/1200Z 15.7N 124.1W 90 KT 105 MPH 72H 07/1200Z 15.6N 126.6W 85 KT 100 MPH 96H 08/1200Z 16.3N 128.2W 80 KT 90 MPH 120H 09/1200Z 17.9N 127.6W 70 KT 80 MPH $$ Forecaster Onderlinde/Cangialosi

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Hurricane Leslie Forecast Discussion Number 33

2018-10-04 16:37:07| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Oct 04 2018 135 WTNT43 KNHC 041437 TCDAT3 Hurricane Leslie Discussion Number 33 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Thu Oct 04 2018 Leslie continues to have an inner area of convection near the center, with a larger convective band present about 120 n mi from the center and additional banding in the northwestern quadrant. Since the last advisory, the central convection has become less symmetric and the eye has become less defined. Based on this and the latest satellite intensity estimates, the initial intensity is nudged downward to 65 kt. While the vertical shear should remain light through the forecast period, the forecast track takes the center away from 26C sea surface temperatures and over 24-25C temperatures, and this should cause a gradual weakening for the next several days. Since there is little change in the guidance, the new intensity forecast is again an update of the previous forecast. The initial motion is now 355/8. In the short term, Leslie will be steered northward with some increase in speed between a mid-level ridge over the central Atlantic and a mid- to upper-level trough seen in water vapor imagery north of Bermuda. A decrease in forward speed should occur from 24-36 h as the trough moves south and a second ridge develops to the west of the tropical cyclone. Beyond 48 h, Leslie is expected to move eastward to east-southeastward at a faster forward speed along the southern edge of the mid-latitude westerlies. The track guidance generally agrees with this scenario, although some spread in both direction and speed appears by 120 h. The new track forecast is similar to the previous forecast and is mostly a blend of the TVCN and HCCA consensus models. Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada on Friday. 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 04/1500Z 32.5N 57.2W 65 KT 75 MPH 12H 05/0000Z 34.1N 57.6W 65 KT 75 MPH 24H 05/1200Z 35.8N 58.1W 60 KT 70 MPH 36H 06/0000Z 36.6N 58.1W 60 KT 70 MPH 48H 06/1200Z 36.8N 56.8W 55 KT 65 MPH 72H 07/1200Z 36.0N 53.5W 50 KT 60 MPH 96H 08/1200Z 35.0N 50.5W 50 KT 60 MPH 120H 09/1200Z 33.5N 47.0W 50 KT 60 MPH $$ Forecaster Beven

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Hurricane Sergio Forecast Discussion Number 20

2018-10-04 10:51:09| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Thu Oct 04 2018 230 WTPZ41 KNHC 040851 TCDEP1 Hurricane Sergio Discussion Number 20 NWS National Hurricane Center Miami FL EP212018 200 AM PDT Thu Oct 04 2018 Sergio's intensity is estimated to have increased just a little more this morning, and it remains a powerful category 4 hurricane. Subjective Dvorak estimates are T6.5/127 kt from TAFB and T6.0/115 kt from SAB, and the initial intensity is raised to 120 kt, which is a blend of these numbers and very close to the latest objective ADT estimate. Sergio's maximum winds are expected to change little over the next 12-24 hours, and the hurricane's intensity could very well be modulated by difficult-to-forecast internal processes such as eyewall replacement cycles. After 48 hours, an increase in shear and gradually cooling sea surface temperatures should result in some weakening, especially when Sergio moves more slowly at the end of the forecast period and possibly upwells some cooler water from below. The updated NHC intensity forecast is nudged downward during the first 48 hours to follow the latest consensus aids, but no changes were made to the previous forecast beyond 48 hours. The hurricane's initial motion is northwestward, or 320/7 kt, with Sergio located along the southwestern periphery of a mid-level ridge extending westward from Mexico. This ridge is expected to build westward and connect to another mid-level ridge located near the central Pacific Ocean, forcing Sergio to turn westward, or even south of due west, between 36-72 hours. By days 4 and 5, a large trough near the west coast of the United States should have greater influence, causing Sergio to slow down and turn northward by the end of the forecast period. The track guidance is tightly clustered for much of the forecast period, although a notable southward shift among the guidance, especially from the ECMWF, required a bit of a southward shift in the official forecast as well. FORECAST POSITIONS AND MAX WINDS INIT 04/0900Z 14.4N 118.8W 120 KT 140 MPH 12H 04/1800Z 15.1N 119.7W 120 KT 140 MPH 24H 05/0600Z 15.8N 121.0W 115 KT 130 MPH 36H 05/1800Z 16.0N 122.2W 105 KT 120 MPH 48H 06/0600Z 15.8N 123.5W 95 KT 110 MPH 72H 07/0600Z 15.5N 126.2W 90 KT 105 MPH 96H 08/0600Z 16.0N 128.5W 80 KT 90 MPH 120H 09/0600Z 17.5N 128.5W 75 KT 85 MPH $$ Forecaster Berg

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Hurricane Leslie Forecast Discussion Number 32

2018-10-04 10:48:05| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Oct 04 2018 546 WTNT43 KNHC 040848 TCDAT3 Hurricane Leslie Discussion Number 32 NWS National Hurricane Center Miami FL AL132018 500 AM AST Thu Oct 04 2018 Leslie has shown no appreciable changes in its structure during the past several hours, and it continues to be a little thin on convection within its eyewall. Another more impressive band of convection extends nearly more than 120 n mi northwest of the center of the ragged eye. The initial intensity remains 70 kt for this advisory, mainly based on a blend of Dvorak CI numbers from TAFB and SAB and an earlier SATCON estimate. Leslie's center has reached sea surface temperatures of 26 degrees Celsius, and these marginal water temperatures are likely to cause a gradual decrease in the cyclone's winds during the next several days. The new NHC intensity forecast is mainly just an update to the previous forecast, largely following the HCCA guidance and the ICON intensity consensus. Leslie continues to move northward, or 350/7 kt, between a shortwave trough south of Nova Scotia and a mid-level ridge over the central Atlantic. This northward motion should continue for the next 36 hours before Leslie becomes trapped between two mid-level highs and is isolated from the mid-latitude westerlies to the north, thus causing its forward motion to nearly stall by 48 hours. By days 3 through 5, Leslie should feel enough influence from the westerlies and an approaching cold front to cause it to move a bit faster toward the east or east-southeast over the north Atlantic. Like the intensity forecast, no major changes were required to the official track forecast, which is merely an update to the previous NHC prediction. Large swells generated by Leslie are expected to continue during the next few days across the southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also begin to increase near the coasts of New England and Atlantic Canada on Friday. 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 04/0900Z 31.4N 57.1W 70 KT 80 MPH 12H 04/1800Z 33.0N 57.3W 65 KT 75 MPH 24H 05/0600Z 35.1N 58.0W 65 KT 75 MPH 36H 05/1800Z 36.3N 58.3W 60 KT 70 MPH 48H 06/0600Z 36.8N 57.7W 60 KT 70 MPH 72H 07/0600Z 36.3N 54.6W 55 KT 65 MPH 96H 08/0600Z 35.5N 51.5W 50 KT 60 MPH 120H 09/0600Z 34.5N 48.0W 50 KT 60 MPH $$ Forecaster Berg

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Hurricane Sergio Forecast Discussion Number 19

2018-10-04 04:36:05| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Wed Oct 03 2018 932 WTPZ41 KNHC 040236 TCDEP1 Hurricane Sergio Discussion Number 19 NWS National Hurricane Center Miami FL EP212018 800 PM PDT Wed Oct 03 2018 Sergio is quite the sight tonight over the eastern Pacific with a large central dense overcast and mesovortices observed within the well-defined eye. Subjective estimates from TAFB and SAB both support a slightly higher initial wind speed of 115 kt on this advisory, which is a good compromise between lower microwave estimates but higher ADT values. Notably, Sergio is the record most 8th category 4 hurricane of the 2018 eastern Pacific season- breaking the old record of 7 set in 2015. Reliable records in the eastern Pacific for major hurricanes go back to 1971. Further strengthening is possible during the next day or so while the shear is forecast to remain low and the water is quite warm. After that time, a combination of cooling waters and higher shear should generally cause Sergio to weaken. This will probably be an unsteady process, however, since eyewall cycles are also likely over the next few days. Overall, the hurricane should be on a weakening trend, and that is the NHC forecast, very similar to the previous one, and a bit higher than the model consensus. Sergio is moving northwest or 315/8. This motion should gradually bend toward the west over the next day or two as the steering flow changes from a ridge near Mexico to a building ridge to the northwest of the hurricane. Sergio could turn to the northwest early next week as the hurricane comes under the influence of a deepening trough over the far eastern Pacific and southwestern United States. The model guidance is in excellent agreement during the next few days, and no significant changes were required to the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 13.8N 118.3W 115 KT 130 MPH 12H 04/1200Z 14.6N 119.1W 120 KT 140 MPH 24H 05/0000Z 15.5N 120.4W 120 KT 140 MPH 36H 05/1200Z 15.9N 121.5W 110 KT 125 MPH 48H 06/0000Z 15.9N 122.8W 100 KT 115 MPH 72H 07/0000Z 15.6N 125.4W 90 KT 105 MPH 96H 08/0000Z 15.8N 128.0W 80 KT 90 MPH 120H 09/0000Z 17.0N 129.0W 75 KT 85 MPH $$ Forecaster Blake

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