Saturday, September 02, 2017

Hurricane Irma: European and American models switch, but a swipe of the mid-Atlantic Coast starts to look more likely

Greg Porter, of the Washington Post Weather Gang, reports evolving concern that Hurricane Irma could hit the US East Coast possibly at Category 4 winds around the eye.  The main link is here

The European and American models seem to have traded places.  American model spaghetti plots tend to suggest likely landfalls along the SE coast, but many European plots turn it out to sea.  High Pressure over the North Atlantic could favor a SE coast landfall.  One model has the storm going up the Chesapeake Bay, which could maintain eyewall windspeeds toward the Beltway.  The most likely day for a landfall looks like around Sept. 12.

But in the pasty European models have been more predictive (as with Sandy).

It is looking less likely that it could go into the Gulf and threaten Louisiana and Texas again. 

A few websites (like Economic Collapse Blog) have claimed that Irma could grow into a record Category 6 as it nears the West Indies.   It would probably lose some strength as it moves north. 

Weatherboy notes the trend of model runs in recent hours. 

The Washington DC area (and perhaps Philadelphia) feel somewhat sheltered by being farther inland/  But, as noted before, a fast moving hurricane could maintain windspeeds as it moved up the Chesapeake Bay, which is 30 miles wide at one point but narrows as it goes north, but mostly very shallow. An eyewall could fit inside the Bay.  Hurricane Hazel in 1954 passed to the west of DC but generated a 98 mph gust at Reagan (then National) airport, although winds off the Potomac may be exaggerated compared to other areas.  I was 11 years old then and remember the event, but I don't remember that there was much destruction or power outages  

People who live about the Fall Line are pretty safe from flooding (unless along Piedmont or mountain streams).  It's desirable to be at least 200 feet above sea level. 
By Image courtesy of Mike Trenchard, Earth Sciences & Image Analysis Laboratory , Johnson Space Center. -, Public Domain, Link

Update: Sept. 6

The latest plots suggest a slightly more Eastern track (Post).  Irma is likely to be slightly off shore for a time until it reaches maybe the Carolinas, which could mean it remains a higher category than it would.  But it may spare FL the worst, as did Matthew.  It is likely to tend to turn farther east as soon as it is farther north at the latitude of the Carolinas.  A hurricane up the west coast of FL could flood Tampa-St. Pete badly because of the construction practices in the past.

Friends in FL (Facebook, etc)  tell me newer high rise condos are built to withstand Cat 4's   

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