BMS Tropical Update 9/24/2017 10 AM CDT

By: - September 24th, 2017

Maria Still Has A U.S. Landfall Threat

I just wanted to provide a quick weekend update on Hurricane Maria and discuss the final end game that will play out this week as it slowly tracks northeast of the Bahamas.  Maria is currently located 300 miles northeast of Great Abaco Island and moving north at 9 mph as a Category 2 hurricane.  Maria is expected to maintain a north to northwest direction of travel until Wednesday of this week.  As suggested in my last update, the National Hurricane Center’s (NHC) cone of uncertainty has expanded to cover the Outer Banks of North Carolina, which means a U.S. landfall is still possible.

Track Guidance

Although the NHC cone of uncertainty is highlighting the risk of landfall along the North Carolina coastline, it seems that there is a 50/50 split in the number of ensemble members from the GFS and ECMWF that have Maria making landfall as opposed to not making landfall.  The landfall probability is currently as high as 50%.  As I mentioned back on September 18th, the end game forecast for Maria would be complicated due to Hurricane Jose, which has now dissipated into open ocean 200 miles southeast of Nantucket, Massachusetts.  Jose has no doubt spared the U.S. from yet another major hurricane landfall this season.

 

 Ensemble Guidance

The ensemble guidance below has been trending to the west with a higher and higher likelihood of landfall.   This trend needs to be watched carefully for a possible landfall on Wednesday this week.  However, after Wednesday, a large scale upper level trough is expected to push Maria out across the north Atlantic.

 

GFS (American) ensemble forecast showing a 40% chance that Maria could track over the Outer Banks of NC before a sharp right turn out to sea.

 

ECMWF (European) ensemble forecast showing several forecasts that track inland to North Carolina before a sharp right turn out to sea. Currently there is a 60% chance of landfall along the Outer Banks.

Intensity

As mentioned, Jose likely has steered Maria away from a southeast U.S. landfall as a major hurricane.  Jose’s slow track will likely also help in decreasing Maria’s intensity later this week, as Maria is expected to follow a similar track to Jose over cooler waters.  Jose has also caused upwelling in these waters, and this is making it more difficult for Maria to maintain its intensity.  I expect fluctuations in Maria’s intensity over the next 36 hours until it reaches some of that colder water.  Also, around Wednesday of this week, wind shear should start to increase from the upper level trough, which should decrease Maria’s intensity.  At this time, I expect Maria to only be a Category 1 hurricane as it moves toward the North Carolina coastline on Wednesday of this week.   It should be noted, however, that Maria is a large cyclone and the associated tropical storm-force winds could eventually reach the North Carolina coastline even if Maria does not make landfall.  It should also be noted that the strongest winds will be on the right side of the storm as it tracks towards North Carolina, so those winds would likely stay off shore.

Insured Loss

A few worst-case scenarios at this time might be Alex 2004 (which did not trigger a PCS Event) and Ophelia 2005, which triggered a $35 million insured loss event.  More recently in 2014, Arthur made landfall on the Outer Banks as a Category 2 hurricane.  Arthur is also the first Category 2 hurricane to make landfall in the U.S. and not be registered as a PCS insured loss event.  At this stage, it’s difficult to understand what type of insured losses to expect from Maria if it tracks close enough to the North Carolina coastline.  Given the current forecast, it should be expected that tropical storm-force winds may be experienced along coastal sections.  Hurricane conditions may be experienced on the Outer Banks, but this will depend on how close Maria tracks to the Outer Banks.  However, as noted above, the strongest winds would still be to the right of the storm center and away from the coastline.  I do expect some areas of the Outer Banks to experience storm surge of up to 8 feet, which could flood some parts of the Outer Banks.

Expected storm surge at Duck Pier, NC showing a storm surge as high as 6 feet.

Next Tropical Troubles

It is that time of year where the African originated storms shut down, and given the current surge of dust off Africa, this seems to likely be the case for at least the near future.

Dust and dry air off Africa now dominate the region

Without any new named storm development since September 16th and with Maria expected to dissipate out to sea later this week after a close interaction with the North Carolina coast, we will have a lull in this very busy season.  Even the busy 2005 hurricane season had a lull, so this season is likely not done yet.  I expect the next area of tropical trouble to develop off the Central American coastline in the western Caribbean later next week, maybe around October 6th.

ECMWF Normalized sea level pressure forecast valid for October 2nd showing Maria off the coast of Nova Scotia, and possible new development off the coastline of Honduras and Nicaragua.

This is one of the very few areas that has not seen tropical activity this season.  The waters here are very warm and the wind shear is low, so the conditions are ripe for more tropical trouble here yet this season.

Current Sea Surface Temperature Anomaly Not the normal to colder than normal along the southeast coastline.

In the meantime, enjoy the lull in this 2017 Atlantic Hurricane Season once Maria turns out to sea later this week .

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