Friday, October 26, 2012

The Perfect Storm 2

In the previous post, which was written on Sunday, I described a scenario that would play out over the next 7 to 10 days.  The details often change significantly at those time frames.  However, the computer models have done a reasonably good job at the overall weather pattern.  The model which has performed the best in my opinion has been the European model at the medium-range.  Now most of the models are clustered toward a similar solution, although the American model (GFS) continues to show some strange results.

The overall pattern is a negatively tilted trough pushing into the eastern part of the country and picking up the northward moving hurricane.  As the two interact Sandy will transform from a tropical cyclone to a nor’easter.  The wind will greatly expand and the storm may become a monster worthy of a Halloween trick.  Sandy will weaken as a hurricane, but may strengthen as a nor’easter before moving into Northeast.

The 500mb forecast pattern by the ECMWF model.  The top chart is for Sunday evening while the bottom chart is for Tuesday morning.  Click on the image for a larger view.  Image Credit: WSI.

The top chart is an analysis of the weather pattern across North American for Thursday evening, October 23, 2012.  Hurricane Sandy is in the lower right.  The bottom chart is a plot of the tracks for Sandy from 00z October 26 to 00z October 30.  Note that the storm system is likely to come ashore anywhere from the Delmarva Peninsula to southern New England.  However, the entire East coast will be affected by the storm.  Image Credit: WLTX-TV.

It is important that the approaching trough be negatively tilted.  If it were positively tilted, the tropical cyclone would accelerate out to sea.  The negative tilt allows the storm to be ventilated causing it to strengthen or maintain its strength.  It also causes the storm to turn toward the northwest then more westward with time.

In addition, there is plenty of warm water to keep the storm powerful into the Northeast.  The storm will draw energy from the warm waters, but the character of the storm will be affected by the winds aloft and the interaction with the upper-level trough.

Hurricane Sandy super-imposed over sea surface temperatures.  The red colored areas are for sea surface temperatures above 79 degrees F.  Image credit: WLTX-TV.

The weather pattern is changing across the entire North American continent.  It is the complex interaction amongst the players which will likely lead to a major nor’easter setting records for parts of the Northeast next Tuesday.  The wind field will be quite large with gale force winds extending out hundreds of miles.  This will increase the fetch of the wind leading to significant coastal flooding, high surf, dangerous conditions at sea, and rip currents along the coast.

The surface forecast for pressure and winds valid Tuesday morning October 30.  The yellow color areas are for winds above 40 knots (46 mph).  Image Credit: NCAR\RAL.

BobHenson at NCAR has researched and written a fine post on how this storm may break records and could be worse than the Perfect Storm in 1991.  It will likely disrupt shipping along the East coast for the next week.  In addition to the coastal concerns there will be some wind damage and power outages inland.  Rainfall could be a problem leading to inland flooding, but I do not think it will be as severe as Irene was last year.

Conditions in South Carolina will begin to undergo changing beginning today.  Clouds and wind will be on the increase.  The wind will become more noticeable on Saturday particularly along the coast.  Winds will be gusting to 40 mph along the coast this weekend.  Inland the winds will not be a real concern until Sunday when the cold front passes through the region.  Winds gusting to 35 and 40 mph will be possible behind the front Sunday through Tuesday.  I will post another blog post later today to update the wind forecasts for the Carolinas through Tuesday.