Friday, October 26, 2012

Hurricane Sandy

Hurricane Sandy is on her way up the eastern seaboard currently as a 75 mph storm.  There's been some gradual weakening over the past 12-24 hours..but that was anticipated.  Expect Sandy's pressure to drop again as she transforms from a tropical to extra-tropical cyclone. She will gain some characteristics of a  Nor'Easter, including the ability to strengthen due to the sharp temperature gradient, while losing the pure warm core circulation.  This will also allow the wind field to expand, much different from a normal tropical system where the strongest winds are wrapped around a compact area near the center of circulation.  Sandy will bring it all to the mid-atlantic and northeast--rain, wind, and even very heavy mountain snows.  So lets jump into my initial thoughts on each of these.

Sandy is a really expansive system, with clouds and rain extending hundreds of miles away.  Here's a satellite image of her yesterday..absolutely massive.

This will cause Sandy to have far reaching effects.  I expect rains to begin as early as late Saturday night across far SE Virginia, getting heavier and spreading farther north and west during the day on Saturday.  Coastal sections will experience their heaviest rains during the mid to late afternoon hours on Sunday as Sandy bypasses to the east.  The heaviest rains will then spread to northern areas of the state as Sandy makes landfall and retrogrades to the west. Right now, I expect areas along and east of I95 to receive anywhere from 4-8" of rain, with isolated areas getting as much as 10".  Farther west, rains won't be quite as heavy, and there will likely be a dramatic precipitation gradient dividing areas that see 5-10" vs those that only see 2-4".  Flash flooding will likely become and issue across areas east of I95 and north of I64.

Winds are also looking to become a major problem from this storm.  Like mentioned above, this storm is going to be different from pure tropical systems.  The wind field is going to expand out hundreds of miles from the center.  I would not be surprised for anywhere from I95 and east to see gusts at times up to 60+mph.  Farther west from there, all the way to the Appalachian Mountains, gusts on the order of 40-50mph are a possibility.  Prepare for down limbs and branches..and many may even lose power.  In the image below, you can already see just how far out tropical storm force winds extend from the center.  Expect this range to even widen as Sandy makes the transition from tropical to extra tropical.  With TS force winds out 200-300 miles from the center, it is not going to take a direct hit to feel the effects.

Snow accumulations is one of the trickiest parts of this forecast.  Strong west/northwest winds wrapping around Sandy will allow cold air to rapidly surge into the southwestern side of the storm as it passes.  As you've probably seen, many of the model runs for the past several days have been showing ridiculous, record breaking snows for portions of western VA, eastern WV, western MD, and SW PA.  These amounts have assumed a 10:1 ratio (which we'll have more on the order of 5:1....maybe as high as 7:1) which have distorted realistic amounts quite a bit.  On top of this, recent temperatures in the 70s and 80s this week have really left a warm ground.  With it only being October, the sun angle is still high.  The combination of these factors will lower amounts quite a bit.  Accumulating snows will be confined mainly to the higher elevations.  The exception will be during the night time hours when we loose daylight, giving snow levels the chance to lower down quite a bit.  With all this being said, I still expect record amounts of snow for some..but it doesn't take the 2-3 feet plus amounts the Euro has been showing to break records.  I dont see any accumulation happening east of the Blue Ridge Mountains..even though there may be a few snow showers as the storm departs and throws some wrap-around moisture into the area.  Some of the higher ridges of WV (above 3000 feet) will possibly see 10-20"...with a good 5-10 for 2000 feet+.  For the Shenandoah Valley...3-6" looks like a decent bet right now..especially above 1500 feet.  If you don't know how high you are...go to in your location...and it will tell you.

Here's my first call map..a lot will depend on track..which right now I believe will make landfall near ACY (atlantic city)...subject to change leading up to the storm.  A second call map will be issued tomorrow around the same time:

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