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Tropical Depression BONNIE Forecast Discussion Number 10

2016-05-30 04:31:39| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT SUN MAY 29 2016 000 WTNT42 KNHC 300231 TCDAT2 TROPICAL DEPRESSION BONNIE DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022016 1100 PM EDT SUN MAY 29 2016 Tropical Depression Bonnie has been meandering over the Low Country of South Carolina this evening. Satellite and radar data indicate that the associated showers and thunderstorms have been shrinking in coverage and are primarily confined to the western side of the circulation over portions of South Carolina, with some outer bands over eastern North Carolina. The circulation of the system has become a little less defined this evening with some evidence of multiple vortices, and the overall appearance of the cyclone is quite ragged. The initial intensity is held at 25 kt, which is a little higher than reports from the nearby surface observations. Bonnie has not moved much since the previous advisory, and the latest initial motion estimate is a south-southeastward drift, or 160/1 kt. The depression should move slowly northeastward or east-northeastward on Monday when a shortwave trough approaches the cyclone. After that time, a slightly faster northeastward or east-northeastward motion is predicted while Bonnie moves along the northwestern side of a subtropical high pressure system. This steering pattern should take the depression, or its remnants, across the coastline of the Carolinas during the next few days and then offshore into the western Atlantic Ocean. The new track forecast has been adjusted a little to the east of the previous one to come into better agreement with the latest GFS and ECMWF consensus. Land interaction during the next few days combined with persistent southerly shear, dry air, and cool waters along the forecast track should prevent Bonnie from restrengthening. The NHC intensity forecast calls for a steady state system through the forecast period, but Bonnie is likely to lose its convective organization and become a remnant low in about two days, or perhaps sooner. Another possibility, however, is that the circulation of the system opens into a trough before it becomes a remnant low. The primary concern from Bonnie continues to be locally heavy rainfall. Isolated rainfall amounts of 6 to 8 inches have been reported in portions of eastern Georgia and southern South Carolina. Additional rainfall amounts of 2 to 3 inches are possible. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 32.8N 80.1W 25 KT 30 MPH...INLAND 12H 30/1200Z 33.1N 79.9W 25 KT 30 MPH...NEAR THE COAST 24H 31/0000Z 33.5N 79.1W 25 KT 30 MPH...NEAR THE COAST 36H 31/1200Z 33.9N 78.4W 25 KT 30 MPH...NEAR THE COAST 48H 01/0000Z 34.4N 77.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/0000Z 35.4N 76.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 03/0000Z 37.0N 74.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 04/0000Z 38.5N 70.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Tropical Depression BONNIE Forecast Discussion Number 8

2016-05-29 16:44:38| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT SUN MAY 29 2016 000 WTNT42 KNHC 291444 TCDAT2 TROPICAL DEPRESSION BONNIE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022016 1100 AM EDT SUN MAY 29 2016 Most of the deep convection associated with the tropical cyclone became separated from the center overnight, and Bonnie weakened to a tropical depression before reaching the south-central coast of South Carolina. Aircraft data indicate that Bonnie made landfall just east of Charleston near the Isle of Palms around 1230 UTC. The tropical cyclone has continued to move faster than expected, with an initial motion estimate of 360/8 kt. The global models insist that a reduction in forward speed will occur today while the cyclone moves around the northwestern portion of a low- to mid-level ridge over the western Atlantic. As a result of the faster forward motion, the NHC forecast track has been adjusted northward accordingly, and now shows the center moving farther inland during the next day or so. After 48 hours, a slightly faster northeastward motion is expected to begin. The updated NHC track is close to the GFS/ECMWF consensus. Bonnie is forecast to weaken some during the next 12 to 24 hours, but little change in strength is expected after that time since a portion of the circulation could be over water. A track farther inland than anticipated would result in a faster rate of weakening, and Bonnie would become a remnant low sooner in this scenario. The primary impact from Bonnie will continue to be locally heavy rainfall, which is occurring over much of eastern Georgia, and portions of the Carolinas. These rains will gradually spread northeastward over the Mid-Atlantic region during the next couple of days. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 33.2N 79.8W 30 KT 35 MPH 12H 30/0000Z 33.6N 79.8W 25 KT 30 MPH 24H 30/1200Z 34.0N 79.5W 25 KT 30 MPH...INLAND 36H 31/0000Z 34.1N 79.0W 25 KT 30 MPH...INLAND 48H 31/1200Z 34.1N 78.3W 25 KT 30 MPH...INLAND 72H 01/1200Z 35.3N 76.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/1200Z 36.5N 74.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 03/1200Z 38.5N 72.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm BONNIE Forecast Discussion Number 7

2016-05-29 10:53:33| National Hurricane Center (Atlantic)

Issued at 500 AM EDT SUN MAY 29 2016 000 WTNT42 KNHC 290853 TCDAT2 TROPICAL STORM BONNIE DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022016 500 AM EDT SUN MAY 29 2016 Shortly after Bonnie reached its peak intensity of 40 kt, water vapor imagery and satellite-derived winds indicate that a surge of 40-60 kt upper-level winds passed over the center of the cyclone, which stripped away all of the associated deep convection. In addition, an intrusion of dry air has inhibited the redevelopment of significant deep convection near the center. Based on the erosion of the convective pattern, the intensity has been lowered to 35 kt for this advisory. Radar and satellite imagery suggest that Bonnie is now moving due north or 360/07 kt. Bonnie has become a more shallow tropical cyclone due to the loss of all deep convection, and the system is expected to be steered generally northward around the western periphery of a low-level ridge for the next 24 hours or so. This should bring the center of Bonnie near or just inland of the South Carolina coast this afternoon or tonight. After that, Bonnie is expected to move slowly northeastward around the northern side of the Bermuda-Azores High and emerge out over the Atlantic by 36 to 48 hours, and continue moving northeastward or east-northeastward through the remainder of the forecast period. The NHC track forecast is similar to the previous advisory track, and closely follows a blend of the GFS and ECMWF model tracks. Continued strong southerly vertical wind shear, along with dry air in the mid- and upper-levels and proximity to land, should prevent any significant restrengthening from occurring. However, there could be intermittent bursts of convection near the center of Bonnie, keeping the cyclone as a tropical storm until landfall occurs later today. By 48 hours and beyond, environmental conditions worsen, and Bonnie is expected to degenerate into a remnant low pressure system by 72 hours, if not sooner. The primary impact from Bonnie will be locally heavy rainfall, which is already occurring over much of South Carolina, eastern Georgia, and portions of southeastern North Carolina. These rains will gradually spread northeastward along the mid-Atlantic region over the next couple of days. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 32.1N 79.4W 35 KT 40 MPH 12H 29/1800Z 32.6N 79.6W 35 KT 40 MPH 24H 30/0600Z 33.3N 79.6W 35 KT 40 MPH...INLAND 36H 30/1800Z 33.5N 78.9W 30 KT 35 MPH...OVER WATER 48H 31/0600Z 33.9N 78.0W 30 KT 35 MPH 72H 01/0600Z 34.5N 76.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/0600Z 35.2N 75.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 03/0600Z 35.8N 74.4W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Tropical Storm BONNIE Forecast Discussion Number 6

2016-05-29 04:36:02| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT SAT MAY 28 2016 000 WTNT42 KNHC 290235 TCDAT2 TROPICAL STORM BONNIE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022016 1100 PM EDT SAT MAY 28 2016 The center of Bonnie has become exposed about 50 n mi to the southeast of a bursting area of deep convection due to strong southerly vertical wind shear. Despite this ragged appearance, data from an Air Force Reserve Hurricane Hunter aircraft mission found some believable SFMR winds northwest of the center that support increasing the initial intensity to 40 kt. Little change in intensity is expected before the center moves near or onto the South Carolina coast on Sunday, with weakening to a tropical depression expected in about 36 hours. Shear, dry air, and cool SSTs should result in Bonnie becoming a remnant low by 72 hours, although I wouldn't be surprised if this occurred a little sooner. Bonnie has moved little since the last advisory, with the 3 most recent aircraft fixes all within about 5 miles of each other. The cyclone should begin to move north-northwestward and then northward during the next 12-24 hours between a mid/upper-level trough advancing into the eastern United States and a building ridge near and west of Bermuda. After that time, a weakening Bonnie should move slowly northeastward through the end of the period. The new NHC forecast is near the previous one through 12 hours. After that time the official NHC track has been adjusted to the right of the previous one but lies left of and a bit slower than the GFS/ECMWF consensus out of respect for continuity. Note that the the shift in the guidance envelope at 24 hours and beyond is largely due to the fact that Bonnie hasn't moved much this evening. The primary impact from Bonnie will be locally heavy rainfall, which is already occurring over portions of coastal South Carolina. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 31.0N 79.5W 40 KT 45 MPH 12H 29/1200Z 31.8N 80.0W 40 KT 45 MPH 24H 30/0000Z 32.7N 80.1W 35 KT 40 MPH...INLAND 36H 30/1200Z 33.1N 79.6W 30 KT 35 MPH...INLAND 48H 31/0000Z 33.5N 78.7W 30 KT 35 MPH...OVER WATER 72H 01/0000Z 34.3N 77.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 02/0000Z 35.0N 76.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 03/0000Z 35.5N 75.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brennan

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Tropical Storm BONNIE Forecast Discussion Number 5

2016-05-28 22:41:36| National Hurricane Center (Atlantic)

Issued at 500 PM EDT SAT MAY 28 2016 000 WTNT42 KNHC 282041 TCDAT2 TROPICAL STORM BONNIE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022016 500 PM EDT SAT MAY 28 2016 A 1431Z ASCAT-B overpass indicated two 34-kt wind vectors existed in the northwest quadrant of the tropical cyclone in a region of deep convection that was not sampled during the earlier reconnaissance mission. Convection briefly weakened, but has redeveloped and persisted in that same part of the storm circulation for the past 5 hours. Furthermore, NOAA Doppler velocity radar data from Charleston and Jacksonville have indicated winds ranging from 50-55 kt between 15,000 and 20,000 feet in the same area of the 34-kt ASCAT wind vectors. Based on these data, the depression has been upgraded to Tropical Storm Bonnie. The initial motion estimate is 320/09 kt. The exposed low-level center near the southeastern edge of the deep convective cloud canopy has been easy to track over the past several hours, and has essentially been moving along the previous forecast track. The NHC model guidance remains in good agreement on Bonnie gradually turning toward the north-northwest as it moves around the west side of a deep-layer ridge, and moving onshore between Charleston and Beaufort, South Carolina, in about 18-24 hours. After landfall a mid-level shortwave trough moving northeastward out of the Mississippi Valley region is expected to significantly weaken the ridge, causing the steering to collapse. The result is that Bonnie is forecast to stall or meander along the coastal region of South Carolina in 24-36 hours before drifting off to the east or northeast by 48 hours. The NHC forecast track is similar to the previous advisory track, and closely follows a blend of GFS and ECMWF models. Bonnie is currently moving over the axis of warmest Gulf Stream sea-surface temperatures of 27-28 deg C. Although slightly cooler shelf water lies ahead of the cyclone, those ocean conditions do not appear to be sufficient to significantly weaken Bonnie based on rather vigorous convection that has developed just offshore of South Carolina today. However, southerly vertical wind shear of at least 20 kt is expected to prevent any rapid or significant intensification before landfall. After 24 hours, land interaction and the aforementioned wind shear should induce slow weakening, although there could be some convective rain bands over water producing wind gusts to tropical-storm force until about 48 hours. The official intensity forecast is similar to the previous advisory and follows the Decay-SHIPS model. The primary impact from Bonnie is expected to be locally heavy rainfall. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 31.1N 79.4W 35 KT 40 MPH 12H 29/0600Z 31.9N 80.1W 40 KT 45 MPH 24H 29/1800Z 32.8N 80.5W 35 KT 40 MPH...INLAND 36H 30/0600Z 33.2N 80.1W 30 KT 35 MPH...INLAND 48H 30/1800Z 33.5N 79.4W 30 KT 35 MPH...INLAND 72H 31/1800Z 34.5N 77.8W 25 KT 30 MPH...INLAND 96H 01/1800Z 35.0N 76.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 02/1800Z 35.7N 75.3W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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