cieldumort
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Loc: Austin, Tx
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Re: Irene Slightly Weaker but Larger and Heading to North Carolina
Fri Aug 26 2011 04:24 PM
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Just a reminder to all when posting to the main page that it is important to stick to facts, and to go light on speculation, rumors, or "gut feelings." There are a number of popular misconceptions with hurricanes (including some outright myths), that get spread around on the Internet during times like now, and the main page is the last place to put them.
With regard to Irene, a few points can not be stressed enough:
* Irene is a very large hurricane with an equally impressive wind field. Generally, the larger the wind field, the greater the potential storm surge (all other variables being equal).
It is inadequate to relate the Saffir-Simpson Scale directly with storm surge, and as such, the NHC has dropped sharing this guide as it has become more a myth, than reality. A very large hurricane can easily produce storm surge one to even three categories above what might typically be found in a mid or small-sized system of equal Category. (Recall Katrina & Ike).
* While winds in most hurricanes in the northern hemisphere do tend to be stronger within the right-front quadrant (northeast quadrant in the case of Irene heading up the east coast), this does not imply that winds will be less dangerous in most if not all other quadrants.
As of this 3:30 PM EDT, verified sustained tropical storm force winds are already occurring just off the coast of South Carolina, well to the northwest of Irene's center. The current wind radius forecast from NHC for 12UTC tomorrow is as follows:
FORECAST VALID 27/1200Z 34.4N 76.6W
MAX WIND 90 KT...GUSTS 110 KT.
64 KT... 80NE 80SE 50SW 50NW.
50 KT...125NE 105SE 75SW 75NW.
34 KT...250NE 200SE 130SW 160NW.
Thus the forecast for 08/27/1200Z is calling for sustained hurricane-fore winds out between 50 and 80 nautical miles in all directions from Irene's center, with high-end tropical storm force winds extending out between 75 and 125 from the center.
* Most tropical cyclone related deaths in the US are now caused by inland flooding.
Even though Irene should be moving forward at an increasing clip, her large size will be accompanied by many hours of rain, some of it very heavy. This persistent rain over a very large area will be falling over parts of the country that have already experienced very excessive rainfall this month. For an example of what can result from this kind of setup, a look at the 1955 Atlantic Hurricane Season is reasonable: ( Wikipedia 1955 Atlantic Hurricane Season ). Inland river flooding became locally catastrophic from back-to-back hurricanes Connie & Diane, a real 1-2 punch.
* Saturated ground gives way easier to effects from strong winds and persistent, heavy rain.
As very large and wet Irene is forecast to spend a good deal of time over ground that has already received copious rainfall, less wind than usual will be all that's required to down trees.
In addition, there will be some increased risk of mudslides along hilly terrain.
* The higher up a building is, the greater the wind speed. A ten story building can easily experience winds a full category higher than a single story structure.
Unlike many other locations that have been hit by hurricanes in recent years, but which have structures no more than a few stories tall, much of the northeast is built skyward.
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