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Hurricane Dorian: Changes in watches and warnings

Hurricane Dorian: Changes in watches and warnings

Dorian continues to exhibit a well-defined eye surrounded by very cold cloud tops on satellite images.  Most tourists had been evacuated from regions in the Bahamas expected to be hit by Hurricane Dorian.

The life-threatening storm surge will raise water levels by as much as 15 to 20 feet above normal tide levels in areas of onshore winds on the Abaco Islands and Grand Bahama Island.  Near the coast, the surge will be accompanied by large and destructive waves.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT as of 7.45  am EST  Sunday, September 1,2019

A Hurricane Warning is in effect for Northwestern Bahamas excluding Andros Island
A Hurricane Watch is in effect for Andros Island
A Tropical Storm Warning is in effect for North of Deerfield Beach to Sebastian Inlet
A Tropical Storm Watch is in effect for north of Golden Beach to Deerfield Beach
A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. Preparations to protect life and property should be rushed to completion.

A Hurricane Watch means that hurricane conditions are possible within the watch area.

A Tropical Storm Warning means that tropical storm conditions are expected 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.

Additional watches or warnings may be required for portions of the east coast of Florida today.

Dorian is expected to produce the following rainfall totals through late this week:
Northwestern Bahamas: 12 to 24 inches, isolated 30 inches.
Coastal Carolinas: 5 to 10 inches, isolated 15 inches.
Central Bahamas and the Atlantic Coast from the Florida peninsula through Georgia…2 to 4 inches, isolated 6 inches. This rainfall may cause life-threatening flash floods.

SURF:  Large swells will affect the east-facing shores of the Bahamas, the Florida east coast, and the southeastern United States coast during the next few days.  These swells are likely to cause life-threatening surf and rip current conditions.

Observations from an Air Force Hurricane Hunter aircraft from several hours ago indicated that the intensity was still near 130 kt, and since the cloud pattern remains very impressive, it is assumed that Dorian has at least maintained that strength through the present time.  The hurricane will remain in a fairly low-shear environment for the next few days, however since it is forecast to move quite slowly over the shallow waters of the northwestern-most Bahamas through Monday, this would likely result in less available oceanic heat content.  Therefore, a very slow weakening is anticipated to commence after 12 hours or so.  The official intensity forecast is near the high end of the numerical guidance suite.

The hurricane continues moving westward, or about 280/7 kt.  A high-pressure ridge to the north of Dorian should maintain this westward movement through today.  By tonight, the global models show the ridge weakening, and this evolution should result in a slowing of the forward speed, with the hurricane becoming nearly stationary around 48 hours.  In comparison to its earlier runs, the new ECMWF track forecast takes the system farther to the west during the next couple of days and is the southwesternmost model through 48 hours.

As a result, the official track forecast has been shifted a little west during that time frame.  In 2 to 4 days, Dorian should turn northward in response to a trough over the eastern United States.

By the end of the period, the flow on the south side of the trough should cause the cyclone to move northeastward near the Carolinas.

The westward shift of the NHC track within the first 48 hours necessitates the change from a Tropical Storm Watch to a Tropical Storm Warning for a portion of the Florida east coast.  Although the official track forecast does not show landfall, users should not focus on the exact track since a Florida landfall is still a distinct possibility.

Key Messages:

A prolonged period of life-threatening storm surge, devastating hurricane-force winds, and heavy rains capable of producing life-threatening flash floods are expected on the Abaco Islands and Grand Bahama through Monday and a hurricane warning is in effect for these areas.

A tropical storm warning is now in effect for a portion of the Florida east coast.  Since Dorian is forecast to slow down and turn northward as it approaches the coast, life-threatening storm surge and dangerous hurricane-force winds are still possible along portions of the Florida east coast by the middle part of this week. Residents should have their hurricane plan in place, know if they are in a hurricane evacuation zone, and listen to advice given by local emergency officials.

There is an increasing risk of strong winds and dangerous storm surge along the coasts of Georgia, South Carolina, and North Carolina later this week.  Residents in these areas should continue to monitor the progress of Dorian.

Heavy rains, capable of producing life-threatening flash floods, are possible over coastal sections of the southeast and lower mid-Atlantic regions of the United States through late this week.

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