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Second weather system ‘steered’, stalled Dorian

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By Amanda Delaney

Forecasting for Hurricane Dorian’s track was a challenge, especially once the system moved into the Eastern Caribbean Sea. 

Dry air and, at the time, Tropical Storm Dorian’s track over St. Lucia disrupted the center of the system. A general west-northwest track was expected with impacts to Puerto Rico, but our confidence lowered in the track when several changes occurred to Tropical Storm Dorian:

  • When Tropical Storm Dorian re-organized, the center of the system was further north.
  • An upper-level low developed and became stationary to the west of Tropical Storm Dorian and drew the system further east than was now forecast toward the U.S. Virgin Islands.
  • Tropical Storm Dorian remained over water for a longer duration and the system strengthened into a hurricane prior to making landfall over the Virgin Islands.

This drastic change to the track lowered the certainty on whether Hurricane Dorian would strike the Northern Bahamas and Florida or turn northwest and impact other areas along the U.S. East Coast.

Although our confidence was lower than average on the track, we were confident that Hurricane Dorian would become a major hurricane with sea surface temperatures that ranged up to 84-88 degrees F east of the Bahamas. Our concerns were that the Western Atlantic high would continue to steer the system more west, over the Northern Bahamas and into Florida. 

However, the ridge weakened while Hurricane Dorian was moving over the Northern Bahamas, and it was several days before a front to the north finally steered the storm to the north.

Unfortunately, this lack of steering is what caused Hurricane Dorian to slow its progress over Great Abaco and stall near Grand Bahama Island as a Category 5 hurricane.

Although Hurricane Dorian weakened into a Category 2 hurricane offshore Florida, warm waters from the Gulf Stream and warmer-than-normal sea surface temperatures near New England and south of Nova Scotia allowed it to maintain its strengthen just prior to making landfall over Nova Scotia.

Here are some additional facts on Hurricane Dorian:

  • Hurricane Dorian tied the strongest sustained winds (160kts) at landfall in the Atlantic with the 1935 Labor Day Hurricane.
  • It was the 5th lowest measured pressure hurricane at landfall in the Atlantic.
  • It was the strongest hurricane ever to impact the Bahamas.

Amanda Delaney is a senior meteorologist with Weather Routing Inc. (WRI). Comments are welcome below.

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