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FLORIDA
STORMS
Potential Tropical Cyclone Nine
LOCATED
320 MI SE OF FREEPORT GRAND BAHAMA ISLAND
WINDS
30 MPH
PRESSURE
1009 MB
MOVING
NW OR 310 DEGREES AT 2 MPH...4 KM/H
From the National Hurricane Center at 1100 PM EDT Thu Sep 12 , 2019
TROPICAL DISTURBANCE MEANDERING OVER THE SOUTHEASTERN BAHAMAS, TROPICAL STORM WATCH ISSUED FOR PORTIONS OF THE FLORIDA EAST COAST,
TAP LINKS BELOW TO FOCUS
key messages
Alerts
hazards
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DISCUSSION

1. The disturbance is expected to become a tropical storm and bring tropical storm force winds to portions of the northwest Bahamas within 36 hours. Note that forecast uncertainty for these disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours.

2. The system is expected to bring tropical-storm-force winds and heavy rainfall to portions of the northwest Bahamas on Friday and Saturday. Significant storm surge is not expected in the northwest Bahamas from this system. Residents there should follow any advice given by local officials.

3. The system could bring tropical-storm-force winds and rainfall to portions of the Florida east coast over the weekend. Residents there should monitor the progress of this system.

1. The disturbance is expected to become a tropical storm and bring tropical storm force winds to portions of the northwest Bahamas within 36 hours. Note that forecast uncertainty for these disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours.

2. The system is expected to bring tropical-storm-force winds and heavy rainfall to portions of the northwest Bahamas on Friday and Saturday. Significant storm surge is not expected in the northwest Bahamas from this system. Residents there should follow any advice given by local officials.

3. The system could bring tropical-storm-force winds and rainfall to portions of the Florida east coast over the weekend. Residents there should monitor the progress of this system.

WHAT'S NEW:

A Tropical Storm Watch has been issued for portions of the coast of eastcentral Florida from Jupiter Inlet northward to the VolusiaBrevard County line.

SUMMARY OF ALERTS:

A Tropical Storm Warning is in effect for...
- Northwestern Bahamas excluding Andros Island

A Tropical Storm Watch is in effect for...
- Jupiter Inlet to VolusiaBrevard County line

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours. Interests elsewhere along the east coast of Florida should monitor the progress of this system. For storm information specific to your area, please monitor products issued by your national meteorological service.

WHAT'S NEW:

A Tropical Storm Watch has been issued for portions of the coast of eastcentral Florida from Jupiter Inlet northward to the VolusiaBrevard County line.

SUMMARY OF ALERTS:

A Tropical Storm Warning is in effect for...
- Northwestern Bahamas excluding Andros Island

A Tropical Storm Watch is in effect for...
- Jupiter Inlet to VolusiaBrevard County line

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours. Interests elsewhere along the east coast of Florida should monitor the progress of this system. For storm information specific to your area, please monitor products issued by your national meteorological service.

WIND: [TOP] Tropical storm conditions are expected within the warning area in the northwest Bahamas by late Friday. Tropical storm conditions are possible in the watch area on the Florida peninsula by Saturday.

RAINFALL: [TOP] The potential tropical cyclone is expected to produce total rainfall accumulations through Sunday:

The Bahamas...3 to 5 inches, isolated maximum amounts around 7 inches.

The U.S. Southeast Coast from central Florida through southeastern Georgia...2 to 4 inches.

STORM SURGE: [TOP] This system is not expected to product significant storm surge in the northwest Bahamas.

WIND: [TOP] Tropical storm conditions are expected within the warning area in the northwest Bahamas by late Friday. Tropical storm conditions are possible in the watch area on the Florida peninsula by Saturday.

RAINFALL: [TOP] The potential tropical cyclone is expected to produce total rainfall accumulations through Sunday:

The Bahamas...3 to 5 inches, isolated maximum amounts around 7 inches.

The U.S. Southeast Coast from central Florida through southeastern Georgia...2 to 4 inches.

STORM SURGE: [TOP] This system is not expected to product significant storm surge in the northwest Bahamas.

At 1100 PM EDT (0300 UTC), the poorly defined center of the disturbance was located by satellite and surface observations near the disturbance was centered near latitude 23.8 North, longitude 74.5 West. The disturbance has been meandering over the southeastern Bahamas. However, the system is expected to move slowly northwestward on Friday, and continue that motion through the weekend. On the forecast track, the system is anticipated to move across the central and northwestern Bahamas on Friday, and along or over the east coast of Florida on Saturday.

Maximum sustained winds are near 30 mph (45 km/h) with higher gusts. The disturbance is forecast to become a tropical depression or a tropical storm during the next day or so.

Environmental conditions are favorable for a tropical depression or tropical storm to form within the next day or two. * Formation chance through 48 hours...high...80 percent * Formation chance through 5 days...high...90 percent

The estimated minimum central pressure is 1009 mb (29.80 inches).

At 1100 PM EDT (0300 UTC), the poorly defined center of the disturbance was located by satellite and surface observations near the disturbance was centered near latitude 23.8 North, longitude 74.5 West. The disturbance has been meandering over the southeastern Bahamas. However, the system is expected to move slowly northwestward on Friday, and continue that motion through the weekend. On the forecast track, the system is anticipated to move across the central and northwestern Bahamas on Friday, and along or over the east coast of Florida on Saturday.

Maximum sustained winds are near 30 mph (45 km/h) with higher gusts. The disturbance is forecast to become a tropical depression or a tropical storm during the next day or so.

Environmental conditions are favorable for a tropical depression or tropical storm to form within the next day or two. * Formation chance through 48 hours...high...80 percent * Formation chance through 5 days...high...90 percent

The estimated minimum central pressure is 1009 mb (29.80 inches).

An Air Force Reserve reconnaissance aircraft earlier this afternoon found a closed but very broad cyclonic circulation along with 1000-ft flight-level and SFMR surface winds that supported an intensity of 25 kt. Recent ship reports also support an intensity of 25 kt, although stronger winds could be present in some of the fragmented convective bands located in the northeastern quadrant.

The initial motion is an uncertain 310/02 kt. The disturbance has been meandering over the southeastern Bahamas the past several hours due to southwesterly mid-/upper-level winds associated with an east-west oriented shortwave trough impinging on the west side of the circulation. A large upper-low located over the central Gulf of Mexico that has produced this shortwave trough is expected to spin out another trough on Friday that will move across South Florida and the Straits, impinging on the disturbance and hindering any significant northwestward motion. By late Friday and Saturday, however, the upper-level is expected to have moved into the western Gulf of Mexico, ending any negative effects in the disturbance. This expected to result in the formation of a tropical cyclone with a deeper vortex column that should get steered basically northwestward in combined deep-layer southeasterly flow between the upper-low to the west and a ridge to the northeast. The new NHC track forecast is basically just an extension of the previous forecast track, albeit a little slower, and lies down the middle of the widely divergent guidance envelope, close to the various simple consensus models, and to the right of the NOAA-HCCA consensus model.

The aforementioned complex steering flow pattern will also play a major role in the intensification process. The two shortwaves troughs are expected to hinder significant convective organization for the next 24-30 hours due to their localized increase in the vertical shear and intrusions of dry air. By 36 hours and beyond, however, those negative factors are forecast to abate, resulting in the disturbance moving underneath an axis of strong upper-level difluence and speed divergence near or just to the east of the Florida east coast. This more favorable upper-level outflow regime should allow for convection to develop and organize fairly quickly around the center before the system reaches the Florida east coast, which should result in the formation of a moderate tropical storm. Although the center is forecast to be inland at 72-96 hours, the center is expected be close enough to the coast to keep tropical-storm-force ongoing over the coastal waters through 120 hours. The official intensity forecast is identical to the previous advisory and follows a blend of the consensus models HCCA and IVCN.

An Air Force Reserve reconnaissance aircraft earlier this afternoon found a closed but very broad cyclonic circulation along with 1000-ft flight-level and SFMR surface winds that supported an intensity of 25 kt. Recent ship reports also support an intensity of 25 kt, although stronger winds could be present in some of the fragmented convective bands located in the northeastern quadrant.

The initial motion is an uncertain 310/02 kt. The disturbance has been meandering over the southeastern Bahamas the past several hours due to southwesterly mid-/upper-level winds associated with an east-west oriented shortwave trough impinging on the west side of the circulation. A large upper-low located over the central Gulf of Mexico that has produced this shortwave trough is expected to spin out another trough on Friday that will move across South Florida and the Straits, impinging on the disturbance and hindering any significant northwestward motion. By late Friday and Saturday, however, the upper-level is expected to have moved into the western Gulf of Mexico, ending any negative effects in the disturbance. This expected to result in the formation of a tropical cyclone with a deeper vortex column that should get steered basically northwestward in combined deep-layer southeasterly flow between the upper-low to the west and a ridge to the northeast. The new NHC track forecast is basically just an extension of the previous forecast track, albeit a little slower, and lies down the middle of the widely divergent guidance envelope, close to the various simple consensus models, and to the right of the NOAA-HCCA consensus model.

The aforementioned complex steering flow pattern will also play a major role in the intensification process. The two shortwaves troughs are expected to hinder significant convective organization for the next 24-30 hours due to their localized increase in the vertical shear and intrusions of dry air. By 36 hours and beyond, however, those negative factors are forecast to abate, resulting in the disturbance moving underneath an axis of strong upper-level difluence and speed divergence near or just to the east of the Florida east coast. This more favorable upper-level outflow regime should allow for convection to develop and organize fairly quickly around the center before the system reaches the Florida east coast, which should result in the formation of a moderate tropical storm. Although the center is forecast to be inland at 72-96 hours, the center is expected be close enough to the coast to keep tropical-storm-force ongoing over the coastal waters through 120 hours. The official intensity forecast is identical to the previous advisory and follows a blend of the consensus models HCCA and IVCN.

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