Tropical Storm Bill

Tropical Storm Bill Track 1100 Hours June 15 2021
Tropical Storm Bill Track 1100 Hours June 15 2021

Tropical Storm Bill Wind Speed ProbabilityTropical Storm BillNWS National Hurricane Center Miami FL 1100 AM AST Tue Jun 15, 2021 (see video below)

Bill remains a fairly well-organized tropical storm. Microwave satellite data indicate that the cyclone still has a fairly tight core and curved bands on the north and west sides of the circulation. However, drier air is wrapping into the southeast portion of the storm, and convection has been decreasing in intensity over the past couple of hours. A very recent ASCAT-A pass showed maximum winds of 45-50 kt southeast of the center. Therefore, the initial intensity is nudged up to 50 kt. The tropical storm is racing northeastward, and the latest initial motion is estimated to be 055/33 kt.

Bill is embedded in the mid-latitude jet stream and a continued fast northeastward motion is expected during the next day or two. This motion should take the storm over much cooler waters on the north side of the Gulf Stream Current in about 12 hours. These cold waters, drier air, and mid-latitude dynamics should cause Bill to transition to an extratropical cyclone later today. All of the models agree that the extratropical cyclone should dissipate in 24 to 36 hours over or near Atlantic Canada. Bill will likely remain at about the same intensity until it dissipates by late Wednesday. It should be noted that given the fast forward speed, most of the strong winds will be on the southeast side of the system.

FORECAST POSITIONS AND MAX WINDS
 
INIT  15/1500Z 40.5N  62.0W   50 KT  60 MPH - Tropical Storm (ESE New York City, NY)
 12H  16/0000Z 43.4N  58.5W   50 KT  60 MPH - Post Tropical (ESE Shelburne, NS Canada)
 24H  16/1200Z 47.5N  54.0W   45 KT  50 MPH - Post Tropical (ESE Placentia Bay, Canada )
 36H  17/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Mon Jun 14, 2021

Deep convection has increased in a cluster to the northeast of the estimated center. Scatterometer measurements showed a couple of 40-41 kt vectors over the southeastern quadrant of the cyclone. On this basis, the estimated intensity is increased to 40 kt, which makes this the second tropical storm of the season, albeit a rather high-latitude one. The system is in an environment of fairly strong southwesterly shear, but the diffluent upper-level flow has apparently contributed to some strengthening in a seemingly hostile environment. Some additional short-term strengthening could occur but by 36 hours, the cyclone should merge with a baroclinic zone while approaching Newfoundland and become extratropical. This transition is also shown by the FSU cyclone phase analyses of the GFS model fields.

Bill is moving fairly swiftly northeastward, or 055/20 kt. The track forecast appears to be straightforward. The flow ahead of a large mid-tropospheric trough near the United States east coast should accelerate the system northeastward for the next day or two, and until the system dissipates. The NHC track forecast is similar to the previous one and not far from the model consensus.

FORECAST POSITIONS AND MAX WINDS
 
INIT  15/0300Z 36.7N  69.8W   40 KT  45 MPH - Tropical Storm (ESE Virginia Beach, VA)
 12H  15/1200Z 38.9N  65.1W   45 KT  50 MPH - Tropical Storm (ESE Atlantic City, NJ)
 24H  16/0000Z 42.6N  59.6W   40 KT  45 MPH - Tropical Storm (ESE Shelburne, NS Canada)
 36H  16/1200Z 46.5N  54.5W   35 KT  40 MPH - Post Tropical (WSW Point Lance, NF Canada)
 48H  17/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM EDT Mon Jun 14, 2021

Satellite and radar images show that the low-pressure area that NHC has been following since yesterday off the coast of North Carolina has become better organized, with a small central dense overcast over the center and more prominent banding features. The low also has advanced ahead of a nearby diffuse stationary front, with that boundary lying northwest of the center. Considering the small core of the low, ample deep convection, satellite pattern, and that the low is feeding off of the thunderstorm activity (and not the front) — it is now classified as a tropical depression. The initial intensity is set to 30 kt, which is our best estimate assuming strengthening from the 20-25 kt overnight ASCAT and surface observations.

The depression is moving northeastward at about 18 kt. A large mid-latitude trough digging across eastern North America should cause the cyclone to continue moving generally northeastward, but faster, over the next couple of days. In about 48 hours, the system is forecast to dissipate near Newfoundland as it is absorbed by a larger extratropical low. Model guidance is in very good agreement on this scenario, and the NHC forecast lies near the track consensus.

The depression has about 24 hours over marginally warm waters in low-to-moderate shear to strengthen before it moves north of the Gulf Stream and decays. Almost all of the intensity guidance shows the system becoming a tropical storm tonight, and considering the healthy initial structure, the official forecast follows that guidance. The low should lose tropical characteristics in about 36 hours due to very cold waters and dissipate near Newfoundland in about 2 days.

FORECAST POSITIONS AND MAX WINDS
 
INIT  14/1500Z 35.0N  73.7W   30 KT  35 MPH - Depression (ENE Morehead City, NC)
 12H  15/0000Z 36.6N  70.9W   40 KT  45 MPH - Tropical Storm (ESE Virginia Beach, VA)
 24H  15/1200Z 39.8N  65.3W   45 KT  50 MPH - Tropical Storm (ENE Atlantic City, NJ)
 36H  16/0000Z 43.6N  59.7W   40 KT  45 MPH - Extra Tropical (ESE Sable Island, NS Canada)
 48H  16/1200Z...DISSIPATED

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Video: Tropical Storm Bill strengthens in the Atlantic; 2 other disturbances being monitored