Friday, August 26, 2011

Size Really DOES Matter...In the Tropics

Whenever there's a hurricane threatening the coast, we tend to focus on the 'strength' of the storm.  How fast will the winds be?  What category hurricane are we talking about? And while those are key issues to consider, something that is often overlooked is the size of the hurricane.

We've had a couple of recent examples of the importance of size as it relates to hurricanes here along the Gulf Coast.  Most notably here in Louisiana, Katrina hammered home that point in 2005.  Consider that Katrina weakened from a rare Category 5 hurricane in the central Gulf to a still strong, but less rare Category 3 by the time it made landfall in LA and MS.  Yet, while it was 'only' a Category 3, Katrina produced a record storm surge along the coast, even surpassing the 'mother' of all hurricanes -- 1969's Camille.  So how did that happen?

    Side-by-side comparison of Camille near landfall (1969) and Katrina near landfall (2005). 

It's all about size, my friends.  At landfall, while Camille had maximum winds around 190 mph (strongest on record for any landfalling U.S. hurricane), the hurricane-force winds only extended about 60 miles from the center.  Katrina, on the other hand, had maximum winds around 125 mph at landfall, but the hurricane-force winds extended out about 120 miles from the center -- twice that of Camille.  The bottom line?  A larger wind field often results in a bigger storm surge, even if the wind speeds aren't as high.

And let's not also forget, a larger wind field simply means more areas and more people get impacted.  Both Katrina and Rita in 2005 had very large wind fields.  Even though Katrina moved well east of metro Baton Rouge and Rita well west of BTR, we had hours of wind gusts in the 50 to 60 mph range.

So, as we continue to follow Irene into the weekend, keep the above points in mind. While Irene may 'only' be a Category 2 hurricane at this point, the size of the wind field will likely result in storm surge and wind damage unlike anything we've seen from a tropical system along the East Coast in a long, LONG time.  And we're not even talking about the heavy rain threat.

Just how big is Irene?  Look at how the wind field compares to other big storms:

Hurricane Extent of T.S. Force Winds (near landfall) Extent of Hurricane Force Winds (near landfall)
Katrina 120 miles 230 miles
Rita 85 miles 205 miles
Ike 120 miles 275 miles
Irene 90 miles 290 miles
Katrina, Rita, & Ike numbers apply for each storm near landfall. Irene wind field numbers from the NHC advisory at 1 p.m. on August, 26, 2011.

NHC graphic showing the large size of Irene's wind field.

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