Tropical Storm Dolly

Post Tropical Storm Dolly Track 1100 Hours June 24 2020
Post Tropical Storm Dolly Track 1100 Hours June 24 2020

Tropical Storm Dolly Wind SpeedsTropical Storm Dolly – National Hurricane Center Miami FL 1100 AM AST Wed Jun 24, 2020 ( new Wed video below)

The center of Dolly has been exposed since last night, and any remaining convection has been displaced well to the system’s south. The circulation is now traversing over waters below 20 degrees C, and therefore is not anticipated that any deep convection will return to the post-tropical remnant low.

The initial intensity of 30 kt is based on an overnight ASCAT overpass. The low is forecast to gradually spin down through tonight and will likely open to a surface trough sometime on Thursday as it continues to move northeastward at around 15 kt.

This is the last NHC advisory on this system.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 42.5N  57.8W   30 KT  35 MPH - Depression (ESE Shelburne, Canada)
 12H  25/0000Z 44.1N  55.7W   25 KT  30 MPH - Depression (ESE Glace Bay, Canada)
 24H  25/1200Z 45.9N  51.5W   25 KT  30 MPH - Low (ESE Biscay Bay, Canada)
 36H  26/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 PM AST Tue Jun 23, 2020 

Dolly’s structure has continued to improve somewhat during the day with convective banding now extending around the eastern and northern side of the circulation. While water vapor imagery indicates that an upper-level low is still in the vicinity of Dolly, that feature is displaced from the cyclone a bit, with some anticyclonic outflow noted in the cirrus canopy. This structure further supports the analysis of Dolly’s transition to a tropical storm. For intensity, there is a wide range among satellite estimates, with TAFB and SAB ranging from 25-35 kt and UW-CIMSS ADT and SATCON estimates between 45-50 kt. The initial intensity will remain 40 kt on this advisory, matching what was shown by the earlier scatterometer data.

Dolly continues to move east-northeastward with an initial motion of 060/10 kt. Strengthening mid-latitude southwesterly flow is expected to cause Dolly to turn northeastward and begin accelerating tonight into Wednesday, and the track guidance is in good agreement on the future path and speed of the storm. Dolly’s future track will take it over much colder waters and into a higher-shear environment over the next day or so, which should cause the cyclone to degenerate into a remnant low on Wednesday. Dissipation is still shown at 48 hours, but global models fields indicate that the circulation could open up before then as the system nears the southeastern tip of Newfoundland.

FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 40.1N  61.1W   40 KT  45 MPH - Tropical Storm (ESE Nantucket, MA)
 12H  24/0600Z 41.2N  59.4W   35 KT  40 MPH - Tropical Storm (ESE Shelburne, Canada)
 24H  24/1800Z 43.1N  56.9W   30 KT  35 MPH - Low (ESE Shelburne, Canada)
 36H  25/0600Z 45.0N  53.8W   25 KT  30 MPH - Low (ESE Poiant Lance, Canada)
 48H  25/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 100 PM AST Tue Jun 23, 2020 

A 1348 UTC ASCAT-A scatterometer pass, arriving just after the previous advisory was issued, indicates that the cyclone is producing winds of 35-40 kt in its southern semicircle. In addition, the radius of maximum winds has contracted to about 40 n mi. This, along with the current convective pattern, suggests that the system has made a transition from a subtropical to a tropical cyclone, and it has been designated as Tropical Storm Dolly.

This Special Advisory package is being issued to update the intensity and wind radii forecasts, increasing Dolly’s maximum winds at each forecast time by 5 kt during the next 24 hours. The forecast track and status changes are the same as in the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1700Z 39.4N  61.7W   40 KT  45 MPH - Tropical Storm (ESE New York City, NY)
 12H  24/0000Z 40.6N  60.3W   35 KT  40 MPH - Tropical Storm (ESE Shelburne, Canada)
 24H  24/1200Z 42.3N  58.1W   30 KT  35 MPH - Depression (ESE Sydney, Canada)
 36H  25/0000Z 44.2N  55.2W   25 KT  30 MPH - Depression (ESE Biscay Bay, Canada)
 48H  25/1200Z...DISSIPATED

National Hurricane Center Miami FL 500 AM AST Tue Jun 23, 2020 

Deep convection has increased during the past several hours in the diurnal convective maximum, although there isn’t much organization to the activity. The depression is situated beneath an upper-level low, and the system has a large radius-of-maximum winds, so it is still subtropical. The initial intensity is 30 kt, based on persistence from the earlier scatterometer data. While it is possible the depression could become a storm later today, rapidly cooling SSTs should cause the system to weaken on Wednesday, and open up into a trough on or before Thursday.

The depression is moving northeastward at about 11 kt. There is good agreement in the track guidance that the system will continue moving in the same general direction with some acceleration during the next couple of days, embedded within the mid-latitude southwesterlies. The new track forecast has been nudged slightly to the north of the previous one, close to the NOAA corrected-consensus model.

FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 39.3N  63.4W   30 KT  35 MPH - Tropical Depression (ESE Atlantic City, NJ)
 12H  23/1800Z 40.0N  61.7W   30 KT  35 MPH - Tropical Depression (ESE New York City, NY)
 24H  24/0600Z 41.4N  59.5W   30 KT  35 MPH - Tropical Depression (ESE Shelburne, Canada)
 36H  24/1800Z 43.3N  56.9W   25 KT  30 MPH - Tropical Depression (ESE Sydney, Canada)
 48H  25/0600Z 45.3N  53.5W   25 KT  30 MPH - Tropical Depression (ESE Biscay Bay, Canada)
 60H  25/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Mon Jun 22, 2020 

The cyclone has little or no deep convection near its center, and remains situated beneath an upper-level low. Therefore, the system is still a subtropical cyclone and the intensity is kept at 30 kt in agreement with the most recent satellite classification from TAFB. The 30-kt intensity was also supported by recent scatterometer data. There is a small window of opportunity for strengthening since the system should remain over a relatively warm Gulf Stream eddy for 12 hours or so. Thereafter, a weakening trend is expected to begin and the system should make the transition to an extratropical cyclone over cooler waters in 36 hours or sooner. The global models indicate that the system should open up into a trough in a couple of days so the official forecast shows dissipation by 72 hours. It would not be surprising if the system meets its demise sooner than that. The official intensity forecast is similar to the latest decay-SHIPS guidance.

The motion continues east-northeastward, or 060/9 kt. Over the next few days, the cyclone should remain embedded in a branch of west-southwesterlies that is split off from the main mid-latitude flow. There is good agreement in the track guidance that the system will turn northeastward with some acceleration during the next 48-60 hours. The official track forecast is similar to the previous one, and is also close to the dynamical model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  23/0300Z 38.7N  64.6W   30 KT  35 MPH - Tropical Depression (ESE Ocean City, MD)
 12H  23/1200Z 39.2N  62.9W   35 KT  40 MPH - Tropical Storm (ESE Atlantic City, NJ)
 24H  24/0000Z 40.3N  60.6W   30 KT  35 MPH - Tropical Depression (ESE New York City, NY)
 36H  24/1200Z 42.0N  58.5W   30 KT  35 MPH - Tropical Depression (ESE Chatham, MA)
 48H  25/0000Z 44.0N  55.5W   25 KT  30 MPH - Tropical Depression (ESE Halifax, Canada)
 60H  25/1200Z 46.0N  52.0W   25 KT  30 MPH - Tropical Depression (ESE Biscay Bay, Canada)
 72H  26/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 PM AST Mon Jun 22, 2020 

The non-tropical low-pressure system that the National Hurricane Center has been following for the past couple of days off of the U.S. east coast has developed enough organized convection near the center to be classified as subtropical depression. The subtropical status is due to the low-level circulation center being co-located beneath an upper-level cold low as seen in water vapor imagery. The initial intensity of 30 kt is based on earlier ASCAT wind data indicating numerous surface wind vectors of 26-28 kt in the southern semicircle, along with a TAFB subtropical satellite classification of ST1.5/25-30 kt.

The initial motion estimate is 075/08 kt. Subtropical Depression Four is located north of a deep-layer ridge and is being influenced by weak westerly mid- to upper-level flow. The cyclone is forecast by all of the global and regional models to move east-northeastward tonight and then turn northeastward on Tuesday. A northeastward motion at a faster forward speed is expected Tuesday night through Thursday when the system is forecast to be located over the cold waters of the far north Atlantic. The cyclone should be absorbed by a larger extratropical low or dissipate on Thursday. The NHC track forecast is close to a blend of the simple consensus aids TVCN and GFEX and the NOAA-HCCA corrected consensus.

The cyclone is beginning to move over a ridge of higher SSTs of 26.0-26.5 deg C in the northern extent of the Gulf Stream. The forecast track takes the subtropical depression down the length of the axis of warmer water during the next 12-18 h, so there is the potential for the cyclone to become a subtropical storm during that time, especially given the large pool of cold air aloft, with 200-mb temperatures of near -58 deg C and 500-mb temperatures of about -10 deg C which is creating a lot of instability. After the system moves off of the warm ridge and into sharply cooler water around 36 hours or so, gradual weakening is expected, with transition to an extratropical cyclone forecast by 48 hours. The NHC intensity forecast closely follows a blend of the consensus models ICON, IVCN, and HCCA.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 38.2N  65.7W   30 KT  35 MPH - Tropical Depression (ESE Ocean City, MD)
 12H  23/0600Z 38.5N  64.0W   35 KT  40 MPH - Tropical Storm (ESE Ocean City, MD)
 24H  23/1800Z 39.0N  62.0W   30 KT  35 MPH - Tropical Depression (ESE Cape May, NJ)
 36H  24/0600Z 40.5N  59.3W   30 KT  35 MPH - Tropical Depression (ESE New York City, NY)
 48H  24/1800Z 42.5N  56.7W   30 KT  35 MPH - Tropical Depression (ESE Shelburne, Canada)
 60H  25/0600Z 45.0N  53.3W   30 KT  35 MPH - Tropical Depression (WSW St.John's, Canada)
 72H  25/1800Z 47.8N  50.4W   30 KT  35 MPH - Tropical Depression (ENE St.John's, Canada)
 96H  26/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 200 PM EDT Mon Jun 22, 2020 

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

1. Shower and thunderstorm activity associated with a well-defined low-pressure system located about 320 miles southeast of Cape Cod, Massachusetts has become better organized today.

The low is moving slowly eastward over the warm waters of the Gulf Stream, and if this recent development trend continues, then a short-lived subtropical depression or subtropical storm could form later today or tonight.  The system is expected to weaken as it moves over cold waters by late Tuesday.

* Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Mon Jun 22, 2020

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

1. Shower activity associated with a large low-pressure system located several hundred miles southeast of Cape Cod, Massachusetts, remains disorganized. The low is moving slowly eastward just north of the warm waters of the Gulf Stream, and tropical or subtropical development will remain unlikely if the system remains over unfavorable ocean conditions. The system is expected to weaken as it moves over even colder waters late today and on Tuesday.

* Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Sun Jun 21, 2020 

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

1. A low-pressure system located several hundred miles southeast of Cape Cod, Massachusetts has become less organized over the past several hours. The low has moved over cold water, north of the Gulf Stream, and tropical or subtropical development has become less likely. The system is expected to weaken as it moves over even colder waters on Monday and Tuesday.

* Formation chance through 48 hours…low…30 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Sun Jun 21, 2020

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

1. A well-defined, non-tropical low-pressure system is located about 300 miles southeast of Cape Cod, Massachusetts. Showers and thunderstorms have recently become a little better organized near the center, and the system could briefly acquire subtropical characteristics tonight and early Monday while the low moves northeastward over the warm waters of the Gulfstream. By Monday night and Tuesday, however, the system is expected to weaken when it moves back over the cooler waters of the North Atlantic.

* Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Sun Jun 21, 2020

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

1. A broad, non-tropical low-pressure system has formed a few hundred miles east of the coast of North Carolina. Although cloudiness and shower activity are currently disorganized, the system could still briefly acquire some subtropical characteristics tonight and early Monday while the low moves northeastward over the warm waters of the Gulfstream. By Monday night and Tuesday, however, the system is expected to weaken when it moves back over the cooler waters of the North Atlantic.

* Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low...20 percent.

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