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Tropical Storm Leslie Forecast Discussion Number 52

2018-10-09 10:57:56| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Oct 09 2018 000 WTNT43 KNHC 090857 TCDAT3 Tropical Storm Leslie Discussion Number 52 NWS National Hurricane Center Miami FL AL132018 500 AM AST Tue Oct 09 2018 Leslie has been steady state overnight. The low-level center is estimated to be on the southern side of a persistent area of deep convection. The satellite intensity estimates are largely unchanged, so the initial intensity is held at 55 kt for this advisory. The tropical storm is moving southeastward at 11 kt steered by the flow on the southwest side of a broad mid- to upper-level trough. This motion, but a slower pace, is expected during the next 24 to 36 hours as the trough pulls away. After that time, another trough is expected to dig southward over the north Atlantic, which should cause Leslie to accelerate east-northeastward. Although the models are in fair agreement for the next few days, they remain in in poor agreement on whether or not the trough will continue to carry Leslie eastward or leave the storm behind around day 5. The GFS and ECMWF have flip flopped, with the GFS now showing Leslie meandering over the east Atlantic by day 5 and the ECMWF moving the system eastward toward Morocco. The ensemble spread remains large in those two global models and there has not been much run-to-run consistency either. The NHC track forecast remains near the various consensus aids, which is usually a good place to be when there is considerable uncertainty like this. Leslie should slowly strengthen during the next few days while it moves over slightly warmer waters and into a more moist environment. These favorable conditions should allow Leslie to become a hurricane once again, likely within a day or two. Weakening is expected to commence this weekend when Leslie is forecast to move over cooler waters and into an atmosphere of stronger shear and drier air, and the system is forecast to become post-tropical by day 5. However, the long range intensity forecast is strongly linked to where Leslie will be, so since the track forecast is uncertain, the intensity prediction is likewise. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 32.2N 43.9W 55 KT 65 MPH 12H 09/1800Z 30.8N 43.1W 55 KT 65 MPH 24H 10/0600Z 29.2N 42.5W 60 KT 70 MPH 36H 10/1800Z 28.1N 42.0W 65 KT 75 MPH 48H 11/0600Z 28.4N 40.5W 65 KT 75 MPH 72H 12/0600Z 31.2N 33.8W 75 KT 85 MPH 96H 13/0600Z 33.5N 23.0W 70 KT 80 MPH 120H 14/0600Z 34.0N 17.0W 55 KT 65 MPH...POST-TROPICAL $$ Forecaster Cangialosi

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Hurricane Michael Forecast Discussion Number 11

2018-10-09 10:57:50| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Tue Oct 09 2018 000 WTNT44 KNHC 090857 TCDAT4 Hurricane Michael Discussion Number 11 NWS National Hurricane Center Miami FL AL142018 400 AM CDT Tue Oct 09 2018 Reports from an Air Force Reserve Hurricane Hunter aircraft a few hours ago indicate that Michael's strengthening has paused, with the maximum winds near 80 kt and a central pressure near 973 mb. The aircraft also reported that the eyewall had become less organized, which may be due to some dry air entrainment and shear. The latest satellite imagery shows the convective banding becoming better defined, and the next aircraft will shortly arrive in the hurricane to provide better information on whether intensification has resumed. The initial motion is now 345/10. There is little change in either the forecast philosophy from the previous advisory, as Michael expected to remain caught between a deep-layer ridge centered off of the U.S. east coast and a highly amplitude mid-latitude trough over the U.S. Plains states and northern Mexico. This pattern should steer the hurricane north-northwestward to northward for the next 24 h or so, followed by a turn to the northeast as Michael recurves into the westerlies. Only minor tweaks have been made to the previous forecast track, with Michael expected to make landfall in the Florida Panhandle on Wednesday and cross the southeastern United States Wednesday night and Thursday. The large-scale models continue to forecast a decrease in the shear later today, and thus Michael is forecast to intensify further before landfall. The new intensity forecast follows the previous forecast in showing Michael as a category 3 hurricane at landfall. The cyclone should weaken significantly as it crosses the southeastern United States, then it should re-intensify over the western Atlantic as it undergoes extratropical transition between 72-96 h. It should be noted that the location and magnitude of peak storm surge flooding is very sensitive to small changes in the track, intensity, and structure of the hurricane. Since there is still uncertainty in all of these parameters, the official NHC storm surge forecast and watch/warning areas includes various plausible scenarios. Regardless of the eventual track and intensity of Michael, life-threatening storm surge inundation is expected along portions of the Florida Panhandle and Big Bend/Nature Coast, and the storm surge watch has been upgraded to a storm surge warning for parts of this area. The NOAA G-IV aircraft is currently conducting a synoptic surveillance mission over the Gulf of Mexico and dropsondes from that mission will be assimilated into the 1200 UTC numerical models runs. Key Messages: 1. Life-threatening storm surge is likely along portions of the coasts of the Florida Panhandle, Big Bend, and Nature Coast, and a storm surge warning is in effect for these areas. Residents in these areas should follow all advice given by their local officials. 2. A hurricane warning has been issued for portions of the Florida Gulf Coast, and everyone in these areas should prepare for life-threatening winds associated with the core of Michael. Damaging winds will also extend inland across portions of the Florida Panhandle, southern Georgia, and southeast Alabama as Michael moves inland. 3. Heavy rainfall from Michael could produce life-threatening flash flooding from the Florida Panhandle and Big Bend region into portions of Georgia and South Carolina. 4. Tropical storm conditions will continue in portions of western Cuba for a few more hours. 5. Michael is expected to produce heavy rainfall and flash flooding over portions of western Cuba during the next day or so. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 24.1N 85.9W 80 KT 90 MPH 12H 09/1800Z 25.7N 86.3W 90 KT 105 MPH 24H 10/0600Z 27.9N 86.4W 100 KT 115 MPH 36H 10/1800Z 29.9N 85.6W 105 KT 120 MPH 48H 11/0600Z 32.3N 83.4W 50 KT 60 MPH...INLAND 72H 12/0600Z 36.5N 75.5W 45 KT 50 MPH...OVER WATER 96H 13/0600Z 42.5N 60.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 14/0600Z 49.0N 40.5W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Hurricane Sergio Forecast Discussion Number 40

2018-10-09 10:38:54| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Tue Oct 09 2018 000 WTPZ41 KNHC 090838 TCDEP1 Hurricane Sergio Discussion Number 40 NWS National Hurricane Center Miami FL EP212018 200 AM PDT Tue Oct 09 2018 Sergio's cloud pattern has changed little in the past 6 hours and is comprised of a fragmented, large outer ring, about 100 n mi in diameter. The coldest cloud tops are now confined to just the southeast portion of cyclone's circulation. The Dvorak satellite intensity estimates from TAFB and SAB support maintaining the initial intensity at 75 kt. Some slow weakening, or possibly very little change in strength, is expected during the next 36 hours as Sergio traverses marginally conducive oceanic temperatures and remains in a low shear surrounding environment. Afterward, the cyclone should enter a region of much cooler sea surface temperatures and increasing southwesterly shear, which should influence significant weakening and reducing Sergio to a tropical storm prior to landfall. Sergio is forecast to move inland over Baja California Sur on Friday and into the northwestern Mexico state of Sonora early Saturday. At the end of the forecast period, Sergio is expected to further degenerate into a remnant low over the southwestern United States. The intensity forecast is weighed heavily on the NOAA-HCCA and the GFS and ECMWF global models which show Sergio making landfall as a tropical storm. Moisture associated with the remnants of Sergio is expected to affect northwestern Mexico and portions of the southwest United States over the weekend and could potentially cause heavy rainfall in this region. For more information about this potential hazard, see products from the Weather Prediction Center and your local NWS forecast office. The initial motion is estimated to be northeastward, or 050/5 kt. Sergio should begin accelerating in the aforementioned direction this morning, and approach the central Baja California peninsula in about 3 days. There is high confidence in the forecast track as the available global and regional models are clustered tightly together through day 5. The NHC forecast lies in the middle of the guidance cluster and is close to the TVCN/HCCA consensus models. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 16.3N 127.9W 75 KT 85 MPH 12H 09/1800Z 16.7N 127.1W 70 KT 80 MPH 24H 10/0600Z 17.6N 125.4W 65 KT 75 MPH 36H 10/1800Z 18.8N 123.2W 65 KT 75 MPH 48H 11/0600Z 20.7N 120.7W 60 KT 70 MPH 72H 12/0600Z 25.1N 114.9W 50 KT 60 MPH 96H 13/0600Z 30.0N 108.4W 35 KT 40 MPH...INLAND 120H 14/0600Z 36.3N 97.9W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Roberts

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Hurricane Michael Forecast Discussion Number 10

2018-10-09 04:57:51| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Mon Oct 08 2018 000 WTNT44 KNHC 090257 TCDAT4 Hurricane Michael Discussion Number 10 NWS National Hurricane Center Miami FL AL142018 1000 PM CDT Mon Oct 08 2018 Data from NOAA and Air Force Reserve hurricane hunter aircraft this evening indicate that Michael has continued to strengthen...despite westerly vertical shear of about 20 kt, which is most unusual. The maximum 8000-ft flight-level winds measured by NOAA so far has been 102 kt and maximum SFMR surface wind speed was 78 kt. The central pressure measured by the two aircraft has been fluctuating between 970 mb and 974 mb, which is likely due to small mesovortices rotating around inside the fairly large 35-nmi-wide eye. Given the aforementioned wind data and the possibility of locally enhanced winds due to the mesovortices, the initial intensity has only been increased to 80 kt rather than 85 kt, which the NOAA flight-level wind data would typically support. The initial motion estimate is 350/11 kt. The steering flow pattern isn't forecast to change much, if at all, for the next 36-48 hours, with Michael expected to remain caught between a deep-layer ridge centered off of the U.S. east coast and a highly amplitude mid-latitude trough over the U.S. Plains states and northern Mexico. The combined deep-layer southerly flow should keep the hurricane moving northward to north-northwestward for the next 36 hours or so. Shortly thereafter and just prior to landfall, the approaching mid-latitude trough is expected to turn Michael toward the north-northeast or northeast. By 48 hours and beyond, significant acceleration toward the northeast ahead of the trough is forecast to continue through the 120-h period, with Michael emerging off of the U.S. mid-Atlantic coast around 96 hours. The new NHC forecast track was nudged slightly to the east of the previous track through 36 h, based on the more eastward initial position and a forward motion that is still to the right or east of short term motion in the model guidance, but is still near the consensus models TVCN, TVCX, and NOAA-HCCA. By 48 hours and beyond, the official track is close to the previous advisory track. Michael's steady intensification over the past 48 hours in the face of 20-kt westerly shear defies traditional logic. Either the shear calculations are unrepresentative or Michael has become more inertially stable due to its large eye and large outer wind field, making it more shear resistant. Having said that, all of the model guidance calls for the shear to decrease to around 10 kt or less by 36 hours, which argues for at least steady intensification during that time given that Michael will be moving over warm SSTs of 28.5C-29C, which are about 1-2 deg C above average for this time of the year. Less-than-normal weakening after landfall in the 48- to 96-h period is expected due to Michael's fast forward speed of 20-30 kt. Re-strengthening as an extratropical low over water on days 4 and 5 is forecast due to baroclinic interaction with a frontal system and the cyclone being back over warm Atlantic waters. The official intensity forecast is a little higher than the consensus models IVCN and HCCA, and is similar to the previous advisory and the FSSE model. It should be noted that the location and magnitude of peak storm surge flooding is very sensitive to small changes in the track, intensity, and structure of the hurricane. Since there is still uncertainty in all of these parameters, the official NHC storm surge forecast and watch/warning areas includes various plausible scenarios. Regardless of the eventual track and intensity of Michael, life-threatening storm surge inundation is expected along portions of the Florida Panhandle and Big Bend/Nature Coast, and the storm surge watch has been upgraded to a storm surge warning for parts of this area. The NOAA G-IV aircraft is currently conducting a synoptic surveillance mission over the Gulf of Mexico and dropsondes from that mission will be assimilated into the 0000 UTC numerical models runs. Key Messages: 1. Life-threatening storm surge is likely along portions of the coasts of the Florida Panhandle, Big Bend, and Nature Coast, and a storm surge warning is in effect for these areas. Residents in these areas should follow all advice given by their local officials. 2. A hurricane warning has been issued for portions of the Florida Gulf Coast, and everyone in these areas should prepare for life-threatening winds associated with the core of Michael. Damaging winds will also extend inland across portions of the Florida Panhandle, southern Georgia, and southeast Alabama as Michael moves inland. 3. Heavy rainfall from Michael could produce life-threatening flash flooding from the Florida Panhandle and Big Bend region into portions of Georgia and South Carolina. 4. Hurricane conditions will continue in portions of western Cuba through this evening, where a hurricane warning is in effect. 5. Michael is expected to produce heavy rainfall and flash flooding over portions of western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 23.2N 85.3W 80 KT 90 MPH 12H 09/1200Z 24.7N 85.9W 90 KT 105 MPH 24H 10/0000Z 26.8N 86.3W 100 KT 115 MPH 36H 10/1200Z 29.1N 85.9W 105 KT 120 MPH 48H 11/0000Z 31.4N 84.4W 55 KT 65 MPH...INLAND 72H 12/0000Z 35.9N 77.3W 45 KT 50 MPH...INLAND 96H 13/0000Z 41.5N 63.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 14/0000Z 47.8N 46.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Hurricane Sergio Forecast Discussion Number 39

2018-10-09 04:41:22| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Mon Oct 08 2018 000 WTPZ41 KNHC 090241 TCDEP1 Hurricane Sergio Discussion Number 39 NWS National Hurricane Center Miami FL EP212018 800 PM PDT Mon Oct 08 2018 Conventional satellite visible and enhanced BD-curve infrared imagery reveal a rather large, curved band feature outlining about 90 percent of what once was an enclosed ragged eye. This primary band is still producing very cold cloud tops, and the satellite intensity estimates have changed little, so the initial intensity will be held at 75 kt for this advisory. Sergio should very slowly spin down during the next 36 hours as it traverses marginally conducive oceanic temperatures. Beyond that period, Sergio should enter a region of much cooler sea surface temperatures and increasing southwesterly shear, which should induce further weakening and at a faster rate. Toward the end of the week, Sergio is forecast to move inland over the central Baja California peninsula and into northernwestern Mexico in 4 days. At which time, the cyclone will quickly weaken and degenerate into a remnant low over the southwestern United States. Moisture associated with the remnants of Sergio is expected to affect northwestern Mexico and portions of the southwest United States over the weekend and could potentially cause heavy rainfall in this region. For more information about this potential hazard, see products from the Weather Prediction Center and your local NWS forecast office. The initial motion is estimated to be northward, or 360/3 kt. Sergio should begin accelerating northeastward Tuesday, and approach the central Baja California peninsula in about 3 days. The NHC forecast is basically an update of the previous one and is close to the various multi-model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 16.0N 128.6W 75 KT 85 MPH 12H 09/1200Z 16.5N 127.7W 70 KT 80 MPH 24H 10/0000Z 17.2N 126.3W 65 KT 75 MPH 36H 10/1200Z 18.2N 124.4W 65 KT 75 MPH 48H 11/0000Z 19.7N 122.1W 60 KT 70 MPH 72H 12/0000Z 24.0N 116.5W 50 KT 60 MPH 96H 13/0000Z 29.3N 109.4W 35 KT 40 MPH...INLAND 120H 14/0000Z 35.4N 99.4W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Roberts

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