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Tropical Storm Dolly Forecast Discussion Number 7

2020-06-24 04:32:49| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Jun 23 2020 000 WTNT44 KNHC 240232 TCDAT4 Tropical Storm Dolly Discussion Number 7 NWS National Hurricane Center Miami FL AL042020 1100 PM AST Tue Jun 23 2020 Dolly's deep convection is diminishing as the cyclone begins to move over colder waters to the north of the Gulf Stream. Given the decreased convection, it is assumed that the circulation is gradually spinning down and the current intensity is therefore estimated to be near 35 kt. This is also consistent with data from a recent scatterometer overpass. Within 24 hours, the system will be moving over SSTs of around 15 deg C, and the cyclone should have degenerated into remnant low devoid of significant convection. The global models forecast the system to open up into a trough in 36 hours or so and the official forest calls for dissipation by 48 hours, if not sooner. The cyclone continues to move east-northeastward, or around 060/9 kt. There is no change to the track forecast reasoning, Dolly is expected to turn northeastward with an increase in forward speed as it moves with the southwesterly mid-level flow to the southeast of the main branch of mid-latitude westerlies. The official track forecast lies close to the previous one and is on top of the latest dynamical model consensus, TVCA, track. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 40.5N 60.3W 35 KT 40 MPH 12H 24/1200Z 41.8N 58.4W 30 KT 35 MPH 24H 25/0000Z 43.9N 55.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 25/1200Z 45.8N 52.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 26/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Dolly Forecast Discussion Number 6

2020-06-23 22:33:42| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Jun 23 2020 000 WTNT44 KNHC 232033 TCDAT4 Tropical Storm Dolly Discussion Number 6 NWS National Hurricane Center Miami FL AL042020 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 12H 24/0600Z 41.2N 59.4W 35 KT 40 MPH 24H 24/1800Z 43.1N 56.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 25/0600Z 45.0N 53.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 25/1800Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Dolly Forecast Discussion Number 5

2020-06-23 18:40:10| National Hurricane Center (Atlantic)

Issued at 100 PM AST Tue Jun 23 2020 000 WTNT44 KNHC 231640 TCDAT4 Tropical Storm Dolly Special Discussion Number 5 NWS National Hurricane Center Miami FL AL042020 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 12H 24/0000Z 40.6N 60.3W 35 KT 40 MPH 24H 24/1200Z 42.3N 58.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 25/0000Z 44.2N 55.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 25/1200Z...DISSIPATED $$ Forecaster Berg

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Subtropical Depression Four Forecast Discussion Number 4

2020-06-23 16:51:03| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Jun 23 2020 000 WTNT44 KNHC 231450 TCDAT4 Subtropical Depression Four Discussion Number 4 NWS National Hurricane Center Miami FL AL042020 1100 AM AST Tue Jun 23 2020 GOES-16 visible satellite imagery shows that the depression's circulation has become better defined since yesterday, and the center is exposed just to the north of a band of convection mainly located within the southern semicircle. This convection is aligned along the Gulf Stream current, where instability is greatest, and the system appears a little more tropical than yesterday. However, the depression is still collocated with an upper-level low, and it will therefore retain the subtropical designation. The initial intensity remains 30 kt based on a ST1.5/25-30 kt classification from TAFB. A partial 1323 UTC ASCAT-B scatterometer pass showed winds near 30 kt to the southeast of the center, and we'll continue to monitor additional scatterometer data to see if there are winds any higher than that. The initial motion is still 11 kt, but the heading has turned east-northeastward at 65 degrees. The depression is forecast to turn back toward the northeast by this evening and begin accelerating on Wednesday within the prevailing mid-latitude flow. This track will take the system over increasingly colder water, placing it over sea surface temperatures less than 20 degrees Celsius by early Wednesday. Those ocean temperatures will make it difficult to support deep convection, and the updated NHC forecast now calls for the system to degenerate to a remnant low in 24 hours. Dissipation has been moved to 48 hours, although global model fields indicate that the system could open up into a trough by 36 hours before it moves past Newfoundland. The Ocean Prediction Center has provided 12-ft sea radii in the southern semicircle based on recent AltiKa and Jason-3 altimeter data. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 39.5N 62.1W 30 KT 35 MPH 12H 24/0000Z 40.6N 60.3W 30 KT 35 MPH 24H 24/1200Z 42.3N 58.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 25/0000Z 44.2N 55.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 25/1200Z...DISSIPATED $$ Forecaster Berg

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Subtropical Depression Four Forecast Discussion Number 3

2020-06-23 10:18:00| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Jun 23 2020 504 WTNT44 KNHC 230817 TCDAT4 Subtropical Depression Four Discussion Number 3 NWS National Hurricane Center Miami FL AL042020 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 12H 23/1800Z 40.0N 61.7W 30 KT 35 MPH 24H 24/0600Z 41.4N 59.5W 30 KT 35 MPH 36H 24/1800Z 43.3N 56.9W 25 KT 30 MPH...POST-TROP/EXTRATROP 48H 25/0600Z 45.3N 53.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 60H 25/1800Z...DISSIPATED $$ Forecaster Blake

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