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Subtropical Storm Beryl Forecast Discussion Number 16

2018-07-14 18:50:05| National Hurricane Center (Atlantic)

Issued at 100 PM AST Sat Jul 14 2018 330 WTNT42 KNHC 141649 TCDAT2 Subtropical Storm Beryl Special Discussion Number 16 NWS National Hurricane Center Miami FL AL022018 100 PM AST Sat Jul 14 2018 The remnants of Beryl have persisted for the past several days, moving through the Bahamas and into the Atlantic between the eastern United States and Bermuda. During the last day or so, the remnants have interacted with an upper-level trough, which has resulted in the redevelopment of a well-defined circulation and organized convection near the center. Recent scatterometer data shows 35 kt winds northeast of the center, so advisories are re-initiated on Beryl. While the strongest winds and convection are relatively close to the center, the upper-level trough is likely contributing baroclinic energy to the system, and thus the regenerated Beryl is being called a subtropical cyclone rather than a tropical cyclone. The initial motion is 035/10. Beryl is in relatively light southwesterly flow between the subtropical ridge and the mid-latitude westerlies, and this pattern should steer the cyclone generally northeastward for the next two to three days. Some increase in forward speed may occur after 36 h as a mid-latitude cyclone approaches from the west. The forecast track is a blend of the HCCA and TVCN consensus models. The forecast track takes Beryl over cold water north of the Gulf Stream in 24 h or less, and the guidance shows little additional intensification during that time. After that, the system should decay over cold water without any extratropical transition. The intensity forecast calls for the system to maintain a 35 kt intensity for 24 hr, followed by weakening and eventual dissipation just after 72 h. FORECAST POSITIONS AND MAX WINDS INIT 14/1700Z 36.4N 65.7W 35 KT 40 MPH...SUBTROPICAL STORM 12H 15/0000Z 37.3N 64.9W 35 KT 40 MPH...SUBTROPICAL STORM 24H 15/1200Z 39.3N 63.7W 35 KT 40 MPH...SUBTROPICAL STORM 36H 16/0000Z 41.2N 61.6W 30 KT 35 MPH...SUBTROPICAL DEPRESSION 48H 16/1200Z 43.4N 58.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 17/1200Z 48.0N 53.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 18/1200Z...DISSIPATED $$ Forecaster Beven

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Post-Tropical Cyclone Chris Forecast Discussion Number 24

2018-07-12 16:59:48| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Jul 12 2018 574 WTNT43 KNHC 121459 TCDAT3 Post-Tropical Cyclone Chris Discussion Number 24 NWS National Hurricane Center Miami FL AL032018 1100 AM AST Thu Jul 12 2018 Extratropical transition has been ongoing for the past few hours, with the rain shield continuing to expand and clouds tops warming in the northwestern semicircle. In addition, surface observations close to the center now show a sharp temperature gradient of almost 20 deg F across the center, which is indicative of the cyclone having merged with a cold frontal system. As a result, Chris has become a post-tropical/extratropical cyclone. The intensity of 60 kt is based on continuity with the previous advisory and earlier ASCAT scatterometer passes. Gradual weakening is forecast by all of the intensity model guidance, but the cyclone is still expected to remain a gale area through 72 hours. Chris has made a slight westward jog, but the latest model guidance insists that the cyclone will start moving back toward the northeast or 045 degrees at 30-31 kt. Post-tropical cyclone Chris is forecast to remain embedded within the fast mid-latitude westerly flow on the east side of a broad, deep-layer trough moving eastward over the northeastern United States and southeastern Canada for the next 48 hours or so. By 72 hours, the cyclone is expected to slow down and begin moving northward as it interacts with a larger mid-latitude upper-level low. The NHC model guidance remains tightly packed, so only minor adjustments to the previous advisory track were required, and mainly in just the first 12 hours. On the forecast track, the center of Chris is expected to pass over or near the Avalon Peninsula of southeastern Newfoundland around 2100-0000 UTC this afternoon and evening. This is the last public advisory issued by the National Hurricane Center on this system. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and available on the Web at https://ocean.weather.gov/shtml/NFDHSFAT1.shtml. Other information on Post-Tropical Cyclone Chris can be found in products issued by Environment Canada/Canadian Hurricane Centre on the internet at weather.gc.ca/hurricane/. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 44.4N 57.7W 60 KT 70 MPH...POST-TROPICAL 12H 13/0000Z 47.7N 52.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 24H 13/1200Z 50.7N 44.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 14/0000Z 53.5N 35.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 14/1200Z 56.5N 26.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 15/1200Z 61.6N 18.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 16/1200Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Chris Forecast Discussion Number 23

2018-07-12 10:33:30| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Jul 12 2018 318 WTNT43 KNHC 120833 TCDAT3 Tropical Storm Chris Discussion Number 23 NWS National Hurricane Center Miami FL AL032018 500 AM AST Thu Jul 12 2018 Deep convection has decreased considerable, and the cloud pattern is taking the typical shape of cyclones during extratropical transition with the rain shield expanding toward the northwest quadrant. Only a small area of thunderstorms remain near the center. Dvorak numbers from TAFB and SAB are decreasing, and assuming that the cyclone has weakened since the last ASCAT pass several hours ago, the initial intensity is set at 60 kt in this advisory. Chris will be moving over much colder waters, and with the increase in shear, the cyclone is forecast to acquire extratropical characteristics as it moves very near the extreme southern portion of Newfoundland later today. After that time, the post-tropical cyclone should continue toward the northeast and become absorbed by a larger cyclone in about 3 or 4 days. Chris is now moving toward the northeast or 045 degrees at 30 kt. The cyclone is already embedded within the fast mid-latitude westerlies, and this flow should continue to steer Chris on this general track until it becomes absorbed. Track models are in excellent agreement in both direction and speed, increasing the confidence in the NHC forecast. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 42.1N 60.1W 60 KT 70 MPH 12H 12/1800Z 45.4N 55.4W 55 KT 65 MPH...POST-TROP/EXTRATROP 24H 13/0600Z 49.0N 48.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 36H 13/1800Z 52.0N 40.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 14/0600Z 54.5N 30.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 15/0600Z 60.0N 20.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 16/0600Z...POST-TROP/EXTRATROP $$ Forecaster Avila

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Hurricane Chris Forecast Discussion Number 22

2018-07-12 04:46:56| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Jul 11 2018 163 WTNT43 KNHC 120246 TCDAT3 Hurricane Chris Discussion Number 22 NWS National Hurricane Center Miami FL AL032018 1100 PM AST Wed Jul 11 2018 Chris is quickly unraveling, with its eye completely disintegrating a few hours ago and the convective pattern showing the hallmarks of the onset of extratropical transition. Earlier microwave data actually showed that the hurricane had a concentric eyewall structure, but the mid-level eye was already being stripped away from the low-level center due to increasing southwesterly shear. Chris's initial intensity is set at 75 kt based on a blend of final T- and CI-numbers from TAFB and SAB. The hurricane is accelerating toward the northeast with an initial motion of 050/25 kt, and the acceleration is expected to continue for the next 48 hours while the cyclone moves ahead of a deep-layer trough located over eastern Canada. After 48 hours, Chris is forecast to slow down to the south of Iceland when it interacts with another deep-layer low. The track guidance is tightly clustered very close to the previous official forecast during the first 72 hours, with only a little more model spread and deviation from the previous forecast at 96 hours. Therefore, the only change to the updated NHC track forecast is to slow down the storm a little on day 4 while it's located south of Iceland. Chris may still exist on day 5, but there's too much uncertainty among the models to extend the official forecast at this point. Chris is currently moving over a few warm eddies along the Gulf Stream, but the hurricane's center will move across the North Wall within the next 6 hours and head toward much colder waters. Vertical shear will also be increasing further over the next 24 hours, and Chris is expected to be fully embedded within a frontal zone within 18-24 hours. The NHC official forecast calls for Chris to complete extratropical transition just before the center reaches extreme southeastern Newfoundland within 24 hours, and the cyclone's intensity should gradually decrease while it moves across the North Atlantic. The intensity forecast is close to the tropical model guidance for the first 12-24 hours but then sides closer to the GFS and ECMWF guidance during the remainder of the forecast. Chris's wind radii have been adjusted slightly based on a 0034 UTC ASCAT pass. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 39.6N 63.0W 75 KT 85 MPH 12H 12/1200Z 42.6N 59.2W 65 KT 75 MPH 24H 13/0000Z 46.9N 52.9W 55 KT 65 MPH...POST-TROP/EXTRATROP 36H 13/1200Z 50.2N 44.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 14/0000Z 53.1N 35.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 15/0000Z 59.6N 21.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 16/0000Z 62.0N 15.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 17/0000Z...DISSIPATED $$ Forecaster Berg

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Hurricane Chris Forecast Discussion Number 21

2018-07-11 22:47:24| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Jul 11 2018 212 WTNT43 KNHC 112047 TCDAT3 Hurricane Chris Discussion Number 21 NWS National Hurricane Center Miami FL AL032018 500 PM AST Wed Jul 11 2018 The eye of Chris has become a little less distinct and more cloud filled during the past few hours, but the overall cloud pattern remains quite impressive in satellite imagery. The respective wind radii were adjusted outward based on a 1454 UTC ASCAT-A overpass, which included one 65-kt surface wind vector in the southeastern quadrant. The initial intensity has been lowered slightly to 80 kt based on a blend of Dvorak intensity estimates of T4.5/77 from both TAFB and SAB, and an ADT estimate of T5.2/95 kt. The initial motion estimate is now 050/22 kt. Little change was made to the previous advisory track. Chris is now embedded within deep southwesterly flow ahead of a broad trough that is digging southeastward along the U.S. Northeast and Mid-Atlantic coasts. The global models are in excellent agreement that the hurricane should continue to accelerate northeastward for the next 72 hours, passing over or near southeastern Newfoundland in 24-36 hours as a strong extratropical cyclone. In contrast to several previous model runs, the latest NHC guidance shows very little cross-track spread or speed differences, and is tightly packed about the previous advisory track. The new forecast track closely follows the previous forecast and the consensus track models HCCA, TVCN, and FSSE. During next 6 hours or so, Chris will be passing over a ocean thermal ridge consisting of SSTs of more than 28 deg C, which is associated with the Gulf Stream. As a result, little change in strength is expected during that time. However, by 24 hours and beyond, the cyclone will be moving over SSTs colder than 12 deg C and encountering southwesterly vertical wind shear in excess of 30 kt, a detrimental combination that will induce rapid weakening and also result in transition to an extratropical cyclone. The new intensity forecast is a little lower than the various intensity model forecasts to account for stronger shear and colder water. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 37.8N 65.7W 80 KT 90 MPH 12H 12/0600Z 40.6N 61.9W 75 KT 85 MPH 24H 12/1800Z 44.9N 56.2W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 13/0600Z 48.8N 49.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 13/1800Z 51.9N 40.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 14/1800Z 58.4N 22.6W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 15/1800Z 63.0N 14.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 16/1800Z...DISSIPATED $$ Forecaster Stewart

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