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Hurricane Sergio Forecast Discussion Number 26

2018-10-05 22:38:25| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Fri Oct 05 2018 000 WTPZ41 KNHC 052038 TCDEP1 Hurricane Sergio Discussion Number 26 NWS National Hurricane Center Miami FL EP212018 200 PM PDT Fri Oct 05 2018 This afternoon's satellite presentation shows that Sergio has become a little better organized. Eyewall cloud temperatures have once again cooled, and the ragged, cloud-filled eye has warmed during the past 6 hours. Accordingly, the subjective and objective T-numbers support increasing the initial intensity to 105 kt for this advisory. As mentioned in this morning's discussion, unforeseen short term inner-core structure changes could cause some intensity fluctuations. Since the environment is forecast to remain favorable during the next 24 hours or so, little change in strength is forecast, and again, the cyclone could become a little stronger than reflected in the forecast. Beyond this period, gradual weakening is expected through day 5 as Sergio moves toward decreasing sea-surface temperatures and into a more stable surrounding environment. The Decay-SHIPS and LGEM intensity guidance, as well as the large-scale models, show increasing southwesterly shear disrupting Sergio's outflow pattern after 72 hours. The intensity forecast is similar to the previous package, and is just above the NOAA-HCCA and IVCN consensus models and below the statistical intensity aids. Sergio's motion is estimated to be west-southwestward, or 250/6 kt within the mid-level steering flow produced by a building high pressure system located north-northeast of the Hawaiian Islands. By early next week, a decrease in forward speed and a turn toward the northwest to north-northwest is forecast as the aforementioned mid-level high retrogrades in response to an amplifying trough over the southwestern United States and Baja California peninsula. Beyond day 3, increasing southwesterly mid-tropospheric flow should induce a northeastward accelerated motion through day 5. The NHC forecast is again adjusted south of the last advisory through 48 hours, and is close to the various multi-model consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 15.7N 122.3W 105 KT 120 MPH 12H 06/0600Z 15.3N 123.1W 105 KT 120 MPH 24H 06/1800Z 14.9N 124.3W 100 KT 115 MPH 36H 07/0600Z 14.8N 125.4W 100 KT 115 MPH 48H 07/1800Z 15.1N 126.3W 90 KT 105 MPH 72H 08/1800Z 16.7N 126.5W 80 KT 90 MPH 96H 09/1800Z 18.9N 123.9W 70 KT 80 MPH 120H 10/1800Z 22.0N 119.3W 65 KT 75 MPH $$ Forecaster Roberts

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Hurricane Sergio Forecast Discussion Number 25

2018-10-05 17:00:20| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Fri Oct 05 2018 000 WTPZ41 KNHC 051500 TCDEP1 Hurricane Sergio Discussion Number 25 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Fri Oct 05 2018 GOES-16 images and a 1054 UTC ATMS microwave overpass indicate that Sergio's 25 n mi eye has become a bit ragged this morning, and has continued to cool. Despite the eye's irregularity, the inner core convection is still intact and is producing very cold (-76C) cloud tops. Primarily due to the eye adjustment temperature, however, the subjective and objective satellite intensity estimates, as well as a recent SATCON analysis, have again decreased to 95-100 kt, and the initial intensity is subsequently lowered to 100 kt. Although due to the possibility of unpredicted inner core structure changes in the short term which could cause Sergio to strengthen again, the current weakening trend is expected to continue through day 5 as Sergio moves toward decreasing oceanic temperatures and into a stabilizing surrounding atmosphere. The statistical intensity guidance as well as the large-scale models show increasing southwesterly shear entering the picture after 72 hours. This should also aid in the forecast weakening trend. The official forecast is just an update of the previous one and follows the NOAA-HCCA consensus and is just above the Florida State Superensemble. Sergio is moving a little left of the previous 6-hr motion...now westward, or 280/7 kt. A gradual turn toward the west-southwest during the next 36 hours is expected as high pressure located north-northeast of the Hawaiian Islands builds to the north of Sergio. Over the weekend, a decrease in forward speed and a turn toward the northwest is forecast as the aforementioned mid-level high retrogrades in response to an amplifying trough over the southwestern United States and Baja California peninsula. Beyond the 72 hour period, increasing southwesterly mid-tropospheric flow should induce a northeastward accelerated motion through the remaining portion of the forecast. The NHC forecast is adjusted a little toward the south of the last advisory through 72 hours to agree more with the various consensus models, but is quite similar in motion and forward speed beyond that period. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 15.9N 121.8W 100 KT 115 MPH 12H 06/0000Z 15.8N 122.7W 95 KT 110 MPH 24H 06/1200Z 15.5N 123.8W 90 KT 105 MPH 36H 07/0000Z 15.2N 125.0W 85 KT 100 MPH 48H 07/1200Z 15.3N 126.0W 85 KT 100 MPH 72H 08/1200Z 16.5N 126.8W 80 KT 90 MPH 96H 09/1200Z 18.5N 125.0W 70 KT 80 MPH 120H 10/1200Z 21.5N 120.8W 60 KT 70 MPH $$ Forecaster Roberts

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Tropical Storm Leslie Forecast Discussion Number 37

2018-10-05 16:43:26| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Oct 05 2018 000 WTNT43 KNHC 051443 TCDAT3 Tropical Storm Leslie Discussion Number 37 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Fri Oct 05 2018 The structure of Leslie has changed little since the last advisory, with a cluster of convection just north of the low-level center and a second cluster well to the southeast of the center. The initial intensity is held at 55 kt based mainly on continuity from earlier scatterometer data, but it is possible that this is a little generous. It should be noted that overall, Leslie has lost some organization since this time yesterday due to the disappearance of the eye and an overall decrease in convective banding. Leslie appears to be slowing its forward speed, with the initial motion now 345/8. A turn to the north and a slower forward speed are expected during the next 12 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. As noted in the previous advisory, there has been a southward shift in the guidance, and the new forecast track is again shifted a little to the south of the previous track. However, it lies to the north of the HCCA and TVCN consensus models. The forecast track takes Leslie over cooler waters around days 2-3, into increasing shear around days 3-4, 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 follows the trend of the previous forecast and the guidance in showing gradual weakening for 48-72 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 southeastern coast of the United States, Bermuda, the Bahamas, and the Greater and Lesser Antilles. These swells will also increase near the coasts of New England and Atlantic Canada later today. 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 05/1500Z 36.2N 58.4W 55 KT 65 MPH 12H 06/0000Z 36.8N 58.1W 50 KT 60 MPH 24H 06/1200Z 37.1N 56.9W 50 KT 60 MPH 36H 07/0000Z 36.9N 54.9W 50 KT 60 MPH 48H 07/1200Z 36.5N 53.0W 45 KT 50 MPH 72H 08/1200Z 35.0N 49.5W 45 KT 50 MPH 96H 09/1200Z 33.0N 45.5W 50 KT 60 MPH 120H 10/1200Z 31.0N 42.5W 50 KT 60 MPH $$ Forecaster Beven

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Tropical Storm Leslie Forecast Discussion Number 36

2018-10-05 10:56:19| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Oct 05 2018 000 WTNT43 KNHC 050856 TCDAT3 Tropical Storm Leslie Discussion Number 36 NWS National Hurricane Center Miami FL AL132018 500 AM AST Fri Oct 05 2018 Leslie's structure has evolved somewhat just within the past 6 hours. Deep convection has redeveloped near the low-level center, although it is displaced a bit to the north due to some southerly shear. The cyclone's circulation remains quite large, and earlier ASCAT data indicated that the radius of maximum winds is about 90-100 n mi away from the center. Since there is some inner-core convection again, the initial intensity remains 55 kt based on the ASCAT data. Leslie has gained some speed and has turned toward the north-northwest, now with an initial motion of 345/12 kt. A general northward motion should continue for the next 12-24 hours, but then Leslie will reach the mid-latitude westerlies and make an abrupt turn toward the east by 36 hours. After that time, Leslie is expected to make some significant eastward progress, although the global models are showing several shortwave troughs in the westerlies imparting a southeastward motion on Leslie by days 4 and 5. In fact, some of the models have shifted significantly southward by the end of the forecast period, leaving the previous official forecast near the northern edge of the guidance envelope. Due to this shift, the new NHC track prediction has been adjusted southward on days 3-5, although it does not yet show as much southward motion as indicated by the normally reliable ECMWF, HCCA, and TVCN multi-model consensus. Leslie doesn't appear to have to contend with much shear during the next 3 days or so, but with such a large wind field mixing the ocean around it, marginal sea surface temperatures are likely to keep the intensity steady. By days 3 and 4, an increase in shear could cause some slight weakening. The models are in very good agreement in showing little to any change in Leslie's intensity during the next 5 days, and that is largely what is indicated in the NHC forecast. 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 increase near the coasts of New England and Atlantic Canada later today. 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 05/0900Z 35.9N 58.3W 55 KT 65 MPH 12H 05/1800Z 36.9N 58.4W 50 KT 60 MPH 24H 06/0600Z 37.4N 57.6W 50 KT 60 MPH 36H 06/1800Z 37.4N 55.8W 50 KT 60 MPH 48H 07/0600Z 37.0N 53.7W 50 KT 60 MPH 72H 08/0600Z 35.7N 49.7W 45 KT 50 MPH 96H 09/0600Z 33.5N 45.5W 45 KT 50 MPH 120H 10/0600Z 31.5N 42.0W 50 KT 60 MPH $$ Forecaster Berg

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Hurricane Sergio Forecast Discussion Number 24

2018-10-05 10:54:21| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Fri Oct 05 2018 000 WTPZ41 KNHC 050854 TCDEP1 Hurricane Sergio Discussion Number 24 NWS National Hurricane Center Miami FL EP212018 200 AM PDT Fri Oct 05 2018 Sergio's eye has cooled somewhat during the past few hours, but there have been no significant changes to the surrounding deep convection. Despite that observation, all available intensity estimates have fallen to between 100-105 kt, and the advisory intensity is therefore set at 105 kt. The gradual weakening trend Sergio has been on is expected to continue for the duration of the forecast period as the hurricane moves toward slightly cooler waters and into a drier, more stable environment. An increase in shear by days 4 and 5 should also help the weakening process along. The updated NHC intensity forecast is not too different from the previous one and is close to the intensity consensus, HCCA, and Florida State Superensemble. Sergio has continued to turn to the left and is now moving west-northwestward, or 290/7 kt. Northerly flow behind a mid-level trough that will swing across the Baja California peninsula will likely push Sergio west-southwestward by 24 hours, and the NHC forecast continues to reflect that scenario. After 48 hours, a break in the ridge left behind by the trough should allow Sergio to turn toward the north by days 3-4. Another shortwave trough is then expected to cause a northeastward acceleration by the end of the forecast period. The GFS and ECMWF, along with the other major track models, have come into better agreement on this acceleration by day 5, and the new official forecast is therefore a little faster than the previous one at that time. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 16.0N 121.2W 105 KT 120 MPH 12H 05/1800Z 16.0N 122.0W 95 KT 110 MPH 24H 06/0600Z 15.7N 123.1W 90 KT 105 MPH 36H 06/1800Z 15.5N 124.3W 85 KT 100 MPH 48H 07/0600Z 15.4N 125.5W 80 KT 90 MPH 72H 08/0600Z 16.3N 126.9W 80 KT 90 MPH 96H 09/0600Z 18.0N 126.0W 70 KT 80 MPH 120H 10/0600Z 20.5N 122.5W 65 KT 75 MPH $$ Forecaster Berg

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