Tropical Storm Debby

Tropical Storm Debby 2000 Hours August 9 2018
Tropical Storm Debby 2000 Hours August 9 2018
Tropical Storm Debby Satellite 2000 Hours August 9 2018
Tropical Storm Debby Satellite 2000 Hours August 9 2018

NWS National Hurricane Center Miami FL 500 PM AST Thu Aug 09 2018

Debby has become post-tropical. The circulation of the cyclone has become ill defined, and it is no longer producing enough organized deep convection to be classified as a tropical cyclone. Therefore, Debby has become post-tropical, and this is the last advisory. The cyclone is accelerating northeastward ahead of a shortwave trough, and this should continue for the next few hours until Debby opens up into a trough of low pressure and merges with a larger frontal boundary later tonight. Debby is likely still producing gale-force winds to the southeast of its center, however all of the guidance indicates that these winds will gradually decrease through early tomorrow.

FORECAST POSITIONS AND MAX WINDS

INIT  09/2100Z 45.5N  40.5W   35 KT  40 MPH...POST-TROPICAL
 12H  10/0600Z...DISSIPATED

NWS National Hurricane Center Miami FL 200 PM EDT Thu Aug 9 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on Tropical Storm Debby, located several hundred miles northwest of the Azores.

Tropical Weather Outlook NWS National Hurricane Center Miami FL 800 PM EDT Wed Aug 8 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: The National Hurricane Center is issuing advisories on Tropical Storm Debby, located about 1100 miles west-northwest of the Azores.

NWS National Hurricane Center Miami FL 1100 AM AST Wed Aug 08 2018

Tropical Storm Debby – The cloud pattern of Debby this morning is definitely typical of a tropical cyclone instead of a subtropical system with moderate convection wrapping around the center, and a well defined upper-level outflow in the eastern semicircle. A blend of the satellite intensity estimates from TAFB and CIMMS SATCON still support an initial intensity of 40 kt. A recent ASCAT pass suggest that this estimate could be generous. Debby is already moving over cooler waters, so a gradual weakening is anticipated before the system becomes extratropical and then gets absorbed by a larger trough. In fact, most of the reliable global models degenerate Debby into a trough of low pressure on Thursday.

The initial motion is toward the northeast or 035 degrees at 10 kt. The cyclone is embedded within a mid-latitude trough, and will continue to move on this general northeastward track with some increase in forward speed in tandem with the trough until dissipation. The track models are in pretty good agreement on this solution.

FORECAST POSITIONS AND MAX WINDS

INIT  08/1500Z 41.2N  48.3W   40 KT  45 MPH - (SE of St.John's, Newfoundland)
 12H  09/0000Z 42.4N  47.2W   35 KT  40 MPH - (SE of St.John's, Newfoundland)
 24H  09/1200Z 44.2N  44.0W   35 KT  40 MPH - (SE of St.John's, Newfoundland)
 36H  10/0000Z 46.5N  39.0W   30 KT  35 MPH...POST-TROP/EXTRATROP
 48H  10/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 AM AST Wed Aug 08 2018

Over the past several hours, deep convection with cloud tops of -55 to -60 deg C has developed in the southeastern semicircle, with some of the convective tops covering the previously exposed low-level circulation center. In addition, outer banding features have dissipated, and an elongated upper-level anticyclone has developed over the cyclone. These convective- and synoptic-scale features indicate that Debby has made the transition from a subtropical to a tropical cyclone.

The initial intensity of 40 kt is based on a blend of UW-CIMSS ADT and SATCON intensity estimates of 39 kt and 42 kt, respectively. Furthermore, the 34-kt wind radii and radius of maximum winds (RMW) were decreased significantly on this advisory based on ASCAT wind data. The initial motion estimate is now 015/08 kt. Debby has made the forecast turn toward the north-northeast, and a further turn toward the northeast is expected later today as the cyclone moves around the northwestern periphery of a deep-layer ridge and ahead of an approaching mid-level trough. The latest model guidance remains in good agreement on this developing track scenario, and the new NHC forecast track is similar to the previous advisory, and lies close to a blend of the track consensus models HCCA and FSSE.

Debby will be moving along a tight sea-surface temperature (SST) gradient for the next 24-36 hours or so, with the northwestern half the circulation being over sub-25C SSTs and the southeastern semicircle being over warmer waters where convection could continue to develop. Given the relatively low vertical wind shear regime that the cyclone will be moving through, along with the possibility of deep convection persisting near the center, the intensity forecast calls for little change in strength today, followed by only slight weakening tonight and early Thursday. By Thursday night or early Friday, SSTs beneath the cyclone are expected to decrease to near 20 deg C and the shear is forecast to increase to more than 20 kt, an unfavorable combination that should result in Debby dissipating over the far north Atlantic by 48 hours.

FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 40.8N  48.8W   40 KT  45 MPH - (SE of St.John's, Newfoundland)
 12H  08/1800Z 41.8N  48.2W   40 KT  45 MPH - (SE of St.John's, Newfoundland)
 24H  09/0600Z 43.2N  46.1W   35 KT  40 MPH - (SE of St.John's, Newfoundland)
 36H  09/1800Z 44.5N  43.4W   30 KT  35 MPH - (SE of St.John's, Newfoundland)
 48H  10/0600Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Tue Aug 07 2018

A little bit of deep convection has developed near the center of Debby, but the overall cloud pattern still resembles more of a subtropical cyclone. Most of the convection is in a ragged band well to the northeast of the center. The initial intensity is held at 35 kt based on a subtropical ST2.5 classification from TAFB. The global models are in good agreement that the system will open up into a trough on the southern side of a large low pressure system within 48 hours.

The initial motion estimate is a slightly slower 360/11 kt. Debby is likely to turn northeastward in the flow on the eastern side of a mid-level trough. The official forecast is somewhat faster than the latest model consensus to maintain some continuity with the previous NHC track.

FORECAST POSITIONS AND MAX WINDS

INIT  08/0300Z 40.3N  49.1W   35 KT  40 MPH -Tropical Storm (ESE of St. John's Newfoundland)
 12H  08/1200Z 41.2N  48.9W   35 KT  40 MPH -Tropical Storm (ESE of St. John's Newfoundland)
 24H  09/0000Z 42.5N  47.5W   35 KT  40 MPH -Tropical Storm (ESE of St. John's Newfoundland)
 36H  09/1200Z 43.9N  44.7W   30 KT  35 MPH -Tropical Storm (ESE of St. John's Newfoundland)
 48H  10/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 800 PM EDT Tue Aug 7 2018

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

The National Hurricane Center is issuing advisories on Subtropical Storm Debby, located a little more than 1000 miles west-northwest of the Azores.

NWS National Hurricane Center Miami FL 500 PM AST Tue Aug 07 2018

Debby’s cloud pattern consists of a cyclonically curved convective band wrapping around a large but somewhat vigorous circulation. TAFB provided a subtropical classification of ST2.5, while an earlier ship located to the east of the center reported 35 kt. These data is used to assign the current intensity of the subtropical cyclone. Although transition to a tropical cyclone is still possible during the next 24 hours, no significant strengthening is anticipated since Debby will soon be moving over cool waters and become fully embedded within a larger mid-latitude trough in a day or so. Debby is forecast to dissipate in about 48 hours or earlier.

The best estimate of the initial motion is toward the north or 355 degrees at 13 kt. The subtropical storm should continue on this general track with a decrease in forward speed for the next 24 hours or so and then turn to the northeast ahead of the trough, which will eventually absorb Debby.

FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 39.7N  49.2W   35 KT  40 MPH - (E of Rhode Island)
 12H  08/0600Z 41.0N  49.5W   35 KT  40 MPH - (E of Massachusetts)
 24H  08/1800Z 42.3N  48.5W   35 KT  40 MPH - (SE of Shelburne, Newfoundland)
 36H  09/0600Z 44.0N  46.0W   30 KT  35 MPH - (SE of Glace Bay, Newfoundland)
 48H  09/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 200 PM EDT Tue Aug 7 2018

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

The National Hurricane Center is issuing advisories on newly formed Subtropical Storm Debby, located a little more than 1000 miles west of the Azores.

NWS National Hurricane Center Miami FL 1100 AM AST Tue Aug 07 2018

The non-tropical low that NHC has been tracking over the North Atlantic for the past few days has developed subtropical characteristics and has been upgraded to subtropical storm status. The tropical-storm-force winds associated with Debby are well removed from the center as indicated by a recent ASCAT pass and are occurring within a cyclonically curved band of moderate convection. Although transition to a tropical cyclone is possible, no significant strengthening is anticipated since the cyclone will soon be moving over cool water and become fully embedded within a larger mid-latitude trough approaching from the west. Debby is expected to dissipate in about 48 hours or earlier.

The best estimate of the initial motion is toward the north or 355 degrees at 14 kt. The subtropical storm should continue on this general track with a decrease in forward speed for the next 24 hours or so and then turn to the northeast ahead of the trough, which will eventually absorb Debby.

FORECAST POSITIONS AND MAX WINDS

INIT  07/1500Z 38.9N  48.5W   35 KT  40 MPH - (SE of St. John's, Newfoundland)
 12H  08/0000Z 41.0N  48.5W   35 KT  40 MPH - (SE of St. John's, Newfoundland)
 24H  08/1200Z 42.7N  48.5W   35 KT  40 MPH - (E of Shelburne, Nova Scotia)
 36H  09/0000Z 44.0N  47.0W   30 KT  35 MPH - (E of Sherbrooke, Nova Scotia)
 48H  09/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 800 PM EDT Mon Aug 6 2018

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

A non-tropical low pressure system centered a little more than 1000 miles west-southwest of the Azores is interacting with an upper- level low, and most of its associated shower activity remains disorganized. Environmental conditions could favor some development during the next day or so, but after that time, the low will encounter increasing cooler waters and development is not anticipated. The low is already moving toward the north-northeast, and this motion should continue for the next several days over the open North Atlantic.
* Formation chance through 48 hours…low…30 percent.
* Formation chance through 5 days…low…30 percent.

We are watching the NE Atlantic for signs of Tropical Storm Debby developing.

NWS National Hurricane Center Miami FL 200 PM EDT Mon Aug 6 2018

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

A non-tropical low pressure system centered about 1100 miles west-southwest of the Azores is interacting with an upper-level low. Although the associated shower and thunderstorm activity has increased during the past 24 hours, environmental conditions are expected to be only marginally conducive for additional development while the system moves north or north-northeastward over the next day or so. The low is forecast to move over cooler waters Tuesday
night, and development is not expected after that time.
* Formation chance through 48 hours…low…30 percent.
* Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Mon Aug 6 2018

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

A non-tropical low pressure system centered about 1200 miles west-southwest of the Azores is interacting with an upper-level low. Although the system is producing disorganized showers and thunderstorms to the east and northeast of the center, environmental conditions are expected to be only marginally conducive for the low
to acquire subtropical or tropical characteristics while it moves north or north-northeastward over the next day or so. The low is forecast to move over cooler waters by Tuesday night, and development is not expected after that time. Additional information on this system can be found in High Seas Forecasts issued by the
National Weather Service. * 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 Aug 5 2018

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

A non-tropical low pressure system centered about 1050 miles west-southwest of the Azores continues to produce limited shower activity. Environmental conditions are expected to be only marginally conducive for the low to acquire subtropical or tropical characteristics while it moves little over the next day or so, and then moves north-northeastward through Tuesday. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Sun Aug 5 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico: A non-tropical low pressure system centered about 1100 miles west-southwest of the Azores continues to produce limited shower activity. Environmental conditions are expected to be only marginally conducive for the low to acquire subtropical or tropical characteristics while it moves little over the next day or so, and then moves north-northeastward through Tuesday. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service.

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

NWS National Hurricane Center Miami FL 800 AM EDT Sun Aug 5 2018

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

A non-tropical low pressure system centered about 1000 miles west-southwest of the Azores continues to produce limited shower activity. Environmental conditions are expected to become marginally conducive for the low to acquire subtropical or tropical characteristics while it moves little over the next day or so, and then moves northeastward through Tuesday. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service.
* Formation chance through 48 hours…low…30 percent.
* Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Sat Aug 4 2018

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

Shower activity associated with a non-tropical low pressure system centered about 950 miles west-southwest of the Azores remains limited. However, the low could gradually acquire subtropical or tropical characteristics while it moves southwestward over the next day or two, and then lifts back to the northeast and remains over warm water through Tuesday.
* Formation chance through 48 hours…low…20 percent.
* Formation chance through 5 days…low…30 percent.

Tropical Weather Outlook NWS National Hurricane Center Miami FL 200 PM EDT Sat Aug 4 2018

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

Shower activity associated with a non-tropical low pressure system centered about 850 miles west-southwest of the Azores remains limited. However, the low could gradually acquire subtropical or tropical characteristics while it moves southwestward over the next day or two, and then lifts back to the northeast and remains over warm water through Tuesday. Additional information on this low pressure area can be found in High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low…30 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Sat Aug 4 2018

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

A non-tropical low pressure system located about 800 miles west-southwest of the Azores is producing gale-force wind gusts northeast of its center. Although associated shower activity is currently limited, the low could gradually acquire subtropical or tropical characteristics over the next few days while it moves southwestward at about 10 mph over warmer water. Additional information on this low pressure area can be found in High Seas Forecasts issued by the National Weather Service.
* Formation chance through 48 hours…low…10 percent.
* Formation chance through 5 days…low...20 percent.

NWS National Hurricane Center Miami FL 200 AM EDT Sat Aug 4 2018

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

A non-tropical low pressure system located about 700 miles west of the Azores is producing gale-force wind gusts northeast of its center. Although associated shower activity is currently limited, the low could gradually acquire subtropical or tropical characteristics over the next few days while it moves southwestward over warmer water. Additional information on this low pressure area can be found in High Seas Forecasts issued by the National Weather Service. * Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low…20 percent.

NWS National Hurricane Center Miami FL 807 AM EDT Mon Jul 9 2018

A tropical wave is along 25W from 03N-19N, moving W at 15 kt. This wave has a good signature at low to mid levels, as confirmed by recent observations and satellite imagery. Scattered showers are noted along the wave’s axis between 08N-12N.

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