Saturday, August 27, 2011

Hurricane Irene Full Update - 10am EDT Saturday

At 10:10 am EDT, radar indicated that the center of Hurricane Irene was located about 25 miles Northeast of Morehead City, NC, and was moving North/Northeast at about 15 mph.  As of the 8am EDT Hurricane Hunter aircraft observation, the minimum central pressure was 28.11 inches of mercury (952 millibars).

Maximum sustained winds by surface reports and radar images were in the 85-90 mph range, with gusts as high as 115 mph having been reported near Cedar Island Ferry Terminal in North Carolina about 90 minutes ago.

The image below shows some preliminary storm reports that have come in across eastern North Carolina.  I've highlighted some of the more significant reports in any given area with the information in the blue text box:

As we've feared for the past several days, the most significant impact so far across North Carolina has come in the form of widespread tree and power line damage due to the combination of strong, damaging winds and rain soaked ground softening the root system of the trees, making it that much easier for them to fall.

Based on surface reports and radar estimates, the map below gives you an idea as to the maximum wind gusts that have been observed across North Carolina so far this morning:

If you divide the above map into thirds going East-West (North Carolina portion only), the winds will begin to taper-off in the Southern third by 12 Noon EDT, the middle third by 3pm EDT and the Northern third by 6pm EDT, as Irene moves slowly North-Northeastward.

As you can see, particularly the middle and Northern two-thirds of eastern North Carolina is in for up to another 8 hours of strong, potentially damaging winds.  Further damage to trees and power lines is likely, and widespread power outages will continue to develop in many areas.

The latest visible (naked eye), infrared (measures cloud temperatures) and water vapor (measures water content) satellite images of Irene are shown below:

Irene remains a well organized system (especially considering the center is now over land), with a very large wind field - particularly the Tropical Storm force wind field, which extends out over 250 miles from the center.  The hurricane force wind field extends out about 90 miles from the center.

The forecast track of Irene has not really changed since my last update yesterday evening.  The official National Hurricane Center (NHC) watch and warning areas also have not really changed.  Hurricane Warnings continue along the red shaded coastline on the image below:

As I mentioned above, Irene is still a very large, powerful hurricane.  The center will emerge back out over water near the North Carolina/Virginia border later this afternoon, which will cease any weakening trend that comes about due to land effects.

Irene is forecast to remain a hurricane well up into New England.  My updated forecast wind impact image is shown below.  The top value in each zone is the sustained wind, with the bottom value the expected maximum wind gusts:

It's important to keep in mind that, due to the size and slow movement of Irene, this will not be a short-lived "gusty wind and then it's gone" type event.  The peak sustained winds and maximum gusts indicated for the above areas will last from 6-9 hours, on average, at any given location.  Keep in mind that less intense but still strong winds and gusts will take place for an additional 4-6 hours at any given location, for a total wind impact time of 10-15 hours.  This is what makes the threat for tree and powerline damage (and resultant power outages) so high.

Also, remember, the wind speeds (both sustained and gusts) in the upper floors (say 25th floor and above) of high-rise buildings will be 20-30% higher than what I've indicated above.

Very heavy, flooding rains will also continue to spread up the East Coast in association with Irene.  Widespread rains of 4-6 inches with localized amounts of 10-12 inches are likely:

In addition to the threat of flooding and flash flooding brought about by the rains, they will continue to make it easier for strong, gusty winds to topple trees and power poles.  Widespread power and other communications outages can be expected along the path of Irene this weekend.

A reminder that all public transportation in the City of New York, as well as many surrounding areas, will be shut down effective 12 Noon today.  This includes all major airports in the New York area.  If you intend to leave town by public transportation and have not done so already, you only have a short time left to take action.  If you have decided to stay home and ride out the storm, make sure to have your severe weather safety kit on hand and ready to go.

Conditions will begin to deteriorate from South to North, first in the Baltimore/Washington areas by late afternoon, the New York City and Long Island areas by this evening, and southern New England later tonight.

For specific local information regarding mandatory and/or voluntary evacuations and potential storm surge, please go to this link and select the National Weather Service office nearest you.

With respect to storm surge, I'll be monitoring the expected time of arrival of Irene to major areas this afternoon and evening (in relation to high tide, etc.) and will give any specific updates as to potential storm surge in those individual posts.  In the meantime, go to the above link for local storm surge forecast details.

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