Tropical cyclone threats 

Posted: 7:20 am Friday, September 7th, 2018

By Kirk Mellish

As expected the tropics sprung to life in September as large-scale hemispheric conditions in atmosphere and ocean became more favorable across the Atlantic Ocean.

As far as FLORENCE is concerned all interests from NORTH FLORIDA TO JERSEY need to monitor future forecasts. People should be prepared now.

System 1 or 2 could be a long term threat to the Caribbean, Florida and/or Gulf Coast, but that is highly speculative at this point and fodder for another day.

Beyond 5 days it is best not to look at any specific model but rather to look at ensemble output and the complete model suite to search for any consensus and to see the full range of possible outcomes and trends.

There are multiple systems to track but the most immediate is FLORENCE, and concern for an East Coast impact continues to grow. It looks like a close encounter at the very least and possibly possibly much worse, specifics TBD.

Historically or climatologically speaking a named storm within 200 miles of Florence Friday AM locale has never even come near the U.S. but have all turned out to sea.

However, mother nature doesn’t care about the past. Such an “analog” approach only works if the weather across the northern hemisphere is fairly “normal” or average. That is increasingly not the case in recent decades. The upper level high pressure ridge north of ‘Flo’ is projected by models to be stronger than normal.

If “FLO” ends up South of Bermuda the threat to land increases, the further north of Bermuda it passes the less the threat, at least in theory.

Bermuda itself has been hit by major hurricanes almost a dozen times since 1871, the strongest 125mph in 1948.

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The key is building high pressure (forecast to be unusually strong, possibly record strength) to the north of the storm blocking an out to sea escape route, as a result eventually it could stall or do loops near or inland the East Coast.

500mb (~18,000ft) jet stream prog ECMWF Ensemble:

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Before any POSSIBLE effect from Florence the remnants of Tropical Storm Gordon combined with a stalled front will cause problems:

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IF, if Florence impacts some of those Mid-Atlantic regions down the road historic flooding could result from heavy rain on top of already saturated soils in that part of the country.

A near-miss and then recurve scenario is still on the table.

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