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Subtropical Storm Alberto Forecast Discussion Number 9

2018-05-27 16:38:12| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun May 27 2018 000 WTNT41 KNHC 271438 TCDAT1 Subtropical Storm Alberto Discussion Number 9 NWS National Hurricane Center Miami FL AL012018 1100 AM EDT Sun May 27 2018 The satellite and radar presentation of Alberto has improved markedly over the past 12 hours or so. Deep convection has increased and become organized in a primary band that wraps around the western and northwestern portions of the storm and the circulation has also become much better defined than 24 hours ago. An Air Force Reserve reconnaissance aircraft has recently indicated that the pressure has fallen to 994 mb. The aircraft has also reported peak flight-level winds of 49 kt and believable SFMR winds of around 40 kt, however, the aircraft has not yet sampled the northwestern portion of the circulation where the deepest convection is located. Assuming that there are slightly higher winds in that area, the initial intensity has been increased to 45 kt. With deep convection closer to the center and a slightly smaller radius of maximum winds, it appears that Alberto is beginning its transition to a tropical cyclone. The reconnaissance aircraft data also indicate that a shallow warm core is present. It is likely that Alberto will make the transition to tropical storm later today or tonight. As this transition occurs, some additional strengthening is forecast while Alberto moves over marginally warm sea surface temperatures and the shear relaxes. However, dry mid- level air wrapping around the eastern portion of the circulation could slow the intensification process before Alberto reaches the coast. The initial motion estimate of 005/12 is again highly uncertain due to the center re-formations that have occurred over the past 12 to 24 hours. The cyclone should move generally northward today, then turn northwestward around the northeastern side of a cutoff low over the central Gulf of Mexico. The timing and location of landfall of the center will be dependent on when the northwestward turn occurs. The latest ECMWF forecast moves Alberto faster northward before it makes the turn and therefore brings the center onshore much sooner and farther eastward than the UKMET and GFS. The NHC forecast is near the model consensus, and is somewhat faster than the previous advisory. Users should remember not to focus on the exact timing and location of landfall since wind and rain will continue to spread northward over the northeastern Gulf Coast well ahead of the center. KEY MESSAGES: 1. Alberto is expected to produce heavy rainfall with a risk of flooding and flash flooding over western Cuba, the Florida Keys, and south Florida today. The risk for heavy rainfall and flooding will then spread over much of the southeast U.S. tonight and Monday. 2. Hazardous storm surge is possible along portions of the eastern Gulf Coast beginning later today, including areas well east of the track of Alberto's center. Residents in the storm surge watch area are encouraged to follow any guidance given by their local government officials. 3. Tropical storm conditions are likely within the tropical storm warning area along the Florida west coast today and within the warning area along the northern Gulf Coast by tonight. 4. Dangerous surf and rip current conditions will continue to affect portions of the eastern and northern Gulf Coast through Monday. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 27.1N 84.4W 45 KT 50 MPH 12H 28/0000Z 28.7N 84.9W 50 KT 60 MPH...TROPICAL STORM 24H 28/1200Z 30.3N 85.9W 50 KT 60 MPH...INLAND 36H 29/0000Z 31.6N 86.4W 35 KT 40 MPH...INLAND 48H 29/1200Z 33.6N 86.7W 25 KT 30 MPH...INLAND 72H 30/1200Z 38.3N 87.2W 20 KT 25 MPH...INLAND 96H 31/1200Z 43.3N 84.7W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 01/1200Z 46.5N 79.5W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Subtropical Storm Alberto Forecast Discussion Number 8

2018-05-27 10:49:41| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun May 27 2018 000 WTNT41 KNHC 270849 TCDAT1 Subtropical Storm Alberto Discussion Number 8 NWS National Hurricane Center Miami FL AL012018 500 AM EDT Sun May 27 2018 Alberto appears a little better organized this morning with an area of deep convection gradually expanding near and to the north of the center. A large band of showers and thunderstorms extends well to the east of the center from western Cuba to south Florida and the northwestern Bahamas. Despite the improved organization, a fairly recent ASCAT pass showed maximum winds of about 35 kt, and therefore, the initial wind speed is held at that value. Based on the system's structure, it still appears to be subtropical, but it is gaining some more tropical characteristics. An Air Force Hurricane Hunter aircraft is scheduled to investigate Alberto later this morning, and should provide a better assessment of its intensity and structure. The initial motion of 015/11 is highly uncertain since the center of the storm has been re-forming and wobbling around. In fact, another center re-formation can not be ruled out since Doppler radar images show a pronounced mid-level circulation to the northeast of the low-level center. Alberto is expected to turn northward later today and then northwestward tonight as it moves around the eastern side of a cutoff mid- to upper-level low over the central Gulf of Mexico. After Alberto merges with the upper low, a turn back to the north is forecast by Monday night and Tuesday. The latest model guidance has shifted notably to the right, and the NHC track forecast has been adjusted by about 30 n mi in that direction. The eastward shift necessitates extending the tropical storm warning along the Gulf coast of Florida. Even though Alberto has not yet strengthened, slow intensification seems likely until it reaches the coastline on Monday. The reasons for intensification consist of diffluence associated with a negatively tilted upper-level trough, lower shear, and marginally warm waters in the Gulf of Mexico. However, the intensity models show a weaker solution this cycle, perhaps because the center may move inland a little sooner, and no model shows Alberto reaching hurricane strength. Based on this guidance, the NHC forecast has been lowered slightly, but it still lies near the high end of the model predictions. Alberto is likely to complete its transition to a tropical storm within 24 hours when it moves into an area of light shear, which should allow the cyclone to develop a deeper warm core and become more symmetric. KEY MESSAGES: 1. Alberto is expected to produce heavy rainfall with a risk of flooding and flash flooding over western Cuba, the Florida Keys, and south Florida through the day. The risk for heavy rainfall and flooding will then spread over many parts of the southeast U.S. tonight and Monday. 2. Hazardous storm surge is possible along portions of the central and eastern Gulf Coast beginning later today, including areas well east of the track of Alberto's center. Residents in the storm surge watch area are encouraged to follow any guidance given by their local government officials. 3. Tropical storm conditions are likely within the tropical storm warning area along the Florida west coast today and within the warning area along the northern Gulf Coast by tonight. 4. Dangerous surf and rip current conditions will likely spread northward along the eastern and northern Gulf Coast through Monday. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 25.0N 84.2W 35 KT 40 MPH 12H 27/1800Z 26.8N 84.4W 40 KT 45 MPH 24H 28/0600Z 28.6N 85.2W 45 KT 50 MPH...TROPICAL STORM 36H 28/1800Z 30.0N 86.0W 50 KT 60 MPH...TROPICAL STORM 48H 29/0600Z 31.7N 86.3W 35 KT 40 MPH...INLAND 72H 30/0600Z 36.2N 86.8W 20 KT 25 MPH...INLAND 96H 31/0600Z 41.1N 85.1W 15 KT 15 MPH...POST-TROP/REMNT LOW 120H 01/0600Z 45.0N 80.5W 15 KT 15 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Subtropical Storm Alberto Forecast Discussion Number 7

2018-05-27 05:08:09| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat May 26 2018 000 WTNT41 KNHC 270307 CCA TCDAT1 Subtropical Storm Alberto Discussion Number 7...Corrected NWS National Hurricane Center Miami FL AL012018 1100 PM EDT Sat May 26 2018 Corrected typo in key message 3 During the past few hours, a burst of convection has formed just north of the low-level center of Alberto, which has caused the center to reform somewhat to the northeast of the previous position. Despite an overall increase in organization, however, reports from an Air Force Reserve Hurricane Hunter aircraft are at best ambiguous on whether the storm has strengthened. The maximum flight-level winds at 925 mb were 45 kt, which would support 30-35 kt at the surface. The maximum SFMR winds outside of the convective burst were 35-37 kt, but since these were higher than the associated flight-level winds it is unclear how reliable they were. In the convection, there were SFMR winds up to near 60 kt which may be due to downbursts and thus are unrepresentative of the strength of the storm. Finally, the central pressure has not fallen since the previous mission and is near 1001 mb. The initial intensity will remain 35 kt, but this could be conservative. In the next 24 h, Alberto should intensify as a subtropical storm due to the influence of a negative-tilt upper-level trough just west of the cyclone. After that time, the trough is forecast to become a cutoff upper-level low, with the center of Alberto near or just north of the low in an area of lighter shear. This evolution should allow the cyclone to develop a deeper warm core and become more symmetric, and this in turn should lead to Alberto transitioning from a subtropical to a tropical storm by 36-48 h. There is little intensity guidance that makes Alberto a hurricane before landfall, so the new intensity forecast keeps the same 55 kt peak and landfall intensities as the previous forecast. After landfall on the northern Gulf Coast, Alberto should steadily weaken over land through the remainder of the forecast period. For the next 12 h or so, Alberto should move generally northward, although some additional eastward reformation of the center remains possible. From 12-48 h, the cyclone should move north-northwestward as it merges with the upper-level low. This should be followed by a northward motion across the southeastern United States from 48-96 h and a subsequent recurvature into the westerlies. The forecast guidance is in good agreement, and the new forecast track is nudged just a little to the east of the previous track. On the current forecast track, Alberto would make landfall near the 48 h point. KEY MESSAGES: 1. Regardless of its exact track and intensity, Alberto is expected to produce heavy rainfall and flash flooding over western Cuba, southern Florida and the Florida Keys. Heavy rainfall and flooding potential will expand to include much of the central U.S. Gulf Coast region and portions of the southeastern United States beginning Sunday and will continue into next week. 2. Hazardous storm surge is possible along portions of the central and eastern Gulf Coast beginning on Sunday, including areas well east of the track of Alberto's center. Residents in the storm surge watch area are encouraged to follow any guidance given by their local government officials. 3. Tropical storm conditions are likely within the tropical storm warning area along the Florida west coast on Sunday and within the warning area along the northern Gulf Coast beginning Sunday night. 4. Dangerous surf and rip current conditions will likely spread northward along the eastern and northern Gulf Coast through Monday. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 23.9N 84.6W 35 KT 40 MPH 12H 27/1200Z 25.9N 84.6W 45 KT 50 MPH 24H 28/0000Z 27.7N 85.6W 50 KT 60 MPH 36H 28/1200Z 28.9N 86.4W 55 KT 65 MPH...TROPICAL STORM 48H 29/0000Z 30.4N 86.8W 55 KT 65 MPH...TROPICAL STORM 72H 30/0000Z 34.5N 87.6W 25 KT 30 MPH...INLAND 96H 31/0000Z 39.0N 86.5W 20 KT 25 MPH...INLAND 120H 01/0000Z 42.5N 82.0W 15 KT 15 MPH...POST-TROPICAL $$ Forecaster Beven

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Subtropical Storm Alberto Forecast Discussion Number 6

2018-05-26 22:52:06| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Sat May 26 2018 000 WTNT41 KNHC 262051 TCDAT1 Subtropical Storm Alberto Discussion Number 6 NWS National Hurricane Center Miami FL AL012018 400 PM CDT Sat May 26 2018 Before departing the storm, the Air Force Reserve Hurricane Hunter aircraft flew near the low-level cloud swirl that became apparent in visible satellite imagery over the southeastern Gulf of Mexico late this morning. Data from the plane indicate that the center had reformed in that location and that the pressure had fallen to 999 mb. The aircraft did not sample the area to the east of the new center, but based on recent satellite classifications and surface observations the initial intensity remains 35 kt for this advisory. The primary mechanism for intensification appears to be a shortwave trough moving southeastward into the larger negatively tilted trough over the eastern Gulf, which should cause a cutoff low to form during the next 24 hours. This is expected to result in deepening of Alberto while it moves generally northward over the Gulf of Mexico on Sunday and Sunday night. The shear is forecast to decrease as Alberto become co-located with the upper-level low and the system could transition to a more tropical cyclone-like structure before landfall. The NHC intensity forecast once again calls for steady strengthening through 36 h, but shows little strengthening after that time due to the possibility of dry air intrusion. The system has moved generally northward during the past 24 hours, however, the reformation of the center today makes the initial motion estimate more uncertain than normal. Alberto should move northward to north-northeastward tonight, and then turn north-northwestward and decelerate on Sunday and Sunday night as it moves around the eastern side of the trough/cutoff low. The dynamical models remain in good agreement on this scenario but have shifted eastward once again. The interpolated guidance models lie a bit west of the model fields due to the more northwestward 1800 UTC initial position of Alberto. As a result, the NHC track is along the eastern edge of the guidance envelope as a compromise between the ECMWF/GFS model fields and trackers. The new NHC track forecast has required the issuance of a Tropical Storm Warning for a portion of the west coast of Florida and a Tropical Storm Warning for a portion of the northern Gulf Coast. KEY MESSAGES: 1. Regardless of its exact track and intensity, Alberto is expected to produce heavy rainfall and flash flooding over western Cuba, southern Florida and the Florida Keys. Rainfall and flooding potential will increase across the central U.S. Gulf Coast region and over much of the southeastern United States beginning Sunday and will continue into next week. 2. Tropical-storm-force winds and hazardous storm surge are possible along portions of the central and eastern U.S. Gulf Coast beginning on Sunday, including areas well east of the track of Alberto's center. Residents in the warning and watch areas are encouraged not to focus on the details of the forecast track of Alberto and should follow any guidance given by their local government officials. 3. Dangerous surf and rip current conditions will likely spread northward along the eastern and northern Gulf Coast through Monday. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 23.3N 85.1W 35 KT 40 MPH 12H 27/0600Z 25.4N 84.9W 45 KT 50 MPH 24H 27/1800Z 27.5N 85.3W 50 KT 60 MPH 36H 28/0600Z 28.9N 86.3W 55 KT 65 MPH...TROPICAL STORM 48H 28/1800Z 30.0N 87.0W 55 KT 65 MPH...TROPICAL STORM 72H 29/1800Z 33.6N 87.9W 30 KT 35 MPH...INLAND 96H 30/1800Z 38.3N 87.5W 20 KT 25 MPH...INLAND 120H 31/1800Z 42.4N 83.4W 15 KT 15 MPH...POST-TROPICAL $$ Forecaster Brown

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Subtropical Storm Alberto Forecast Discussion Number 5

2018-05-26 16:45:02| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sat May 26 2018 000 WTNT41 KNHC 261444 TCDAT1 Subtropical Storm Alberto Discussion Number 5 NWS National Hurricane Center Miami FL AL012018 1100 AM EDT Sat May 26 2018 There has been an increase in convection to the east and southeast of the center of Alberto this morning, however, the overall organization of the system has not changed much. Visible satellite imagery and recent reconnaissance aircraft data suggest that the circulation is somewhat elongated and a new low-level center could be forming just northwest of the western tip of Cuba. As suggested by the global models there could be several re-formations of or a discontinuity in the track of the low-level center today. Although there have been no recent observations to support the 35-kt intensity, the intensity is held at that value since the aircraft has not sampled the area well east of the center and due to the overall increase in convection. A shortwave trough dropping southeastward over the northwestern Gulf of Mexico is expected to sharpen the larger negatively tilted trough over the eastern Gulf, which is expected to cause the cyclone to deepen during the next 24 to 36 hours. This trend is consistent with the global model guidance which unanimously strengthen Alberto through Sunday. After that time, Alberto is expected to be co-located with the upper-level low which should result in some decrease in shear and a possible transition to a more tropical cyclone-like structure. The NHC intensity forecast calls for steady strengthening, but only the ECMWF-based SHIPS guidance brings Alberto near hurricane strength before landfall. Steady weakening should occur after the center moves inland. Alberto is moving northward to north-northeastward at about 9 kt. The cyclone should continue on this general heading today, but it is expected to turn north-northwestward and slow down on Sunday and Sunday night as it interacts with the mid- to upper-level trough/low over the Gulf. The track guidance has shifted slightly eastward this cycle and the NHC forecast has been adjusted accordingly. The new NHC track is near a blend of the ECMWF and GFS models, but it is not as far east as the UKMET or the TVCA multi-model consensus. The eastward adjustment in the track forecast has required the issuance of a tropical storm watch for a portion of the west coast of Florida and an eastward nudge of the watch along the coast of the Florida panhandle. KEY MESSAGES: 1. Regardless of its exact track and intensity, Alberto is expected to produce heavy rainfall and flash flooding over western Cuba, southern Florida and the Florida Keys. Rainfall and flooding potential will increase across the central U.S. Gulf Coast region and over much of the southeastern United States beginning Sunday and will continue into next week. 2. Tropical-storm-force winds and hazardous storm surge are possible along portions of the central and eastern U.S. Gulf Coast beginning on Sunday, including areas well east of the track of Alberto's center, and tropical storm and storm surge watches are in effect for portions of these areas. Residents in the watch areas are encouraged not to focus on the details of the forecast track of Alberto and should follow any guidance given by their local government officials. 3. Dangerous surf and rip current conditions are affecting portions of the Yucatan Peninsula and western Cuba and will likely spread along the eastern and central U.S. Gulf Coast later today and tonight. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 21.6N 84.9W 35 KT 40 MPH 12H 27/0000Z 23.8N 84.6W 40 KT 45 MPH 24H 27/1200Z 26.0N 85.1W 45 KT 50 MPH 36H 28/0000Z 27.4N 86.0W 50 KT 60 MPH...TROPICAL CYCLONE 48H 28/1200Z 28.7N 86.6W 55 KT 65 MPH...TROPICAL CYCLONE 72H 29/1200Z 31.6N 87.7W 40 KT 45 MPH...INLAND 96H 30/1200Z 35.6N 88.2W 25 KT 30 MPH...INLAND 120H 31/1200Z 39.0N 85.0W 20 KT 25 MPH...INLAND $$ Forecaster Brown

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