Saturday, September 24, 2011

Impact risk (satellite debris): 1 in 20 trillion
Landfall risk (surprise storm): 2 in ten

11:15 PM EDT 9/24/11  (UPDATE) The National Hurricane Center has lowered the probability for development of the system to 20% as shown in the graphic. However, our team remains on alert for the possibility this situation develops into a surprise soaking for areas that need it the least. Consider what took place almost one year ago. Though we don't expect a situation akin to what NOAA called an "Unholy Matrimony"it bears close monitoring just to make sure.

September 30, 2010 produced a surprise soaking in the eastern Mid-Atlantic many will not soon forget. Those along the I-95 corridor and Mid-Atlantic coast may recall that remnants of Tropical Storm Nicole, which only lasted 6 hours as a named system, but became embedded in a similar looking frontal boundary. In a matter of 12 hours, all the moisture feeding into this boundary swept over the Washington-Baltimore-Philadelphia metro areas, dropping 6-9" of rain on millions of people... and the news media was befuddled as to what it should be called. It wasn't a Tropical Depression, nor a Tropical Storm, but the pouring rain sure did act like it. In a matter of hours, hundred of roads were blocked, schools were closing early and frantic parents could not even get to the schools. (Image: NOAA's GOES-13 Satellite capture of the 9/30/10 event)

The difference between then and now? In September 2010, the Mid-Atlantic had just come off a glorious 2 weeks of sunshine and blue skies when the remnants of non-Tropical Storm Nicole struck. Much of the region was in a drought from the Carolinas to Maryland. This year, those same areas have received 10-14" of rain for all of September. Mind you, that is not counting Hurricane Irene, which was August! 

So what could happen? Our multi-state Tropical Team has analyzed the situation and has prepared this PRELIMINARY OVERVIEW in a  "Low/Medium/High" breakdown of the possibilities. Invest 91L will be impacting the coast of the Carolinas and the Mid-Atlantic early this week as either as energy embedded in a frontal boundary, a Tropical Depression or weak Tropical Storm. Here's our Team's "FootPrint" on the storm (Forecasters Daniel, Jason, Ross, Greg; Advisors Mr. Foot and Mr. Krichinsky)

Least Case Scenario: 91L makes it's way north, slightly farther to the east, dropping a maximum of 1.5'' of rain in a concentrated area around the Outer Banks and Southern VA.

Mid-Range Scenario: 91L follows the NHC track (brushing the coast), but does not develop into a named tropical system, but still dumps up to 2.5'' of rain along the Outer Banks of NC and over an inch along the DelMarVa peninsula and southern New Jersey. We see this as the most likely of the three scenarios.
Worst Case Scenario: 91L tracks a bit more to the west, over the Gulf Stream and intensifies into a  ~40mph Tropical Storm, bringing rain amounts up to 3.5'' along the Carolina coast and over 2'' into the DelMarVa peninsula as well as strong gusty winds.

(FIRST REPORT) 6:30 PM EDT 9/24/11 While the media and sky watchers have been concerned about the risk of a 6.5 ton satellite falling to Earth today, our Tropical Team has been keeping tabs on a far greater risk that may surprise A LOT more  people. No, this is not unfounded hype over newly minted Tropical Storm Philippe, but an issue much closer to home.  U.S. computer model guidance shown by Colorado State University indicates an area of disturbed weather north of the Bahamas is may reach the North Carolina coast within 24-36 hours. This system, identified as "Invest 91L" is denoted by the National Hurricane Center with a 30% chance of development in the next 48 hours. Take a look at the enhanced satellite imagery and see if you detect some unusual activity in this system, which might be behind the NHC's rationale for bumping this up.

What we think this means.  
If CSU model plots, Day 1-3 rainfall projections from NOAA's Hydrometeorological Prediction Center, and this surface analysis from the Ocean Prediction Center are taken 48 hours, areas from Eastern North Carolina to the southern Delmarva could be facing a surprise dose of heavy tropical rain. Let's hope it stays just that. Recent storm history is replete with famous sayings of "it's just a tropical depression" (Gaston, Richmond, 2004); "Was not even a hurricane" (Isabel, Baltimore, 2003); or "A minimal hurricane" (Irene, New York City, 2011).

What happens next. 
The bigger issue for public safety and emergency management officials will be become what comes after this event. Fresh off another "Lee-like" deluge this weekend, the East coast's tropical river of rain may actually get worse. For the week ahead, the triple squeeze of (1) Above-normal sea surface temperatures in the Gulf of Mexico; (2) A westward push of the Atlantic ridge; and 3) Eastward push of several low pressure systems in the Midwest could fuel another round of widespread inland flooding rain, severe storms and coastal flooding. If Invest 91L decides to go against atmospheric conventions (tropical systems NEVER do that!) and develop prior to landfall, it would surprise a LOT of folks who are not even expecting a tropical system near the U.S.  

Our Tropical Team will be collaborating on the situation this evening, check back later tonight on our threat assessment for  this system in the 48 hour period ahead. (Forecasters Foot, Salter and the Tropical Team) 


juleew said...

Am I going BACK to the store for batteries and candles?  I used up THIRTY ONE candles in the last storm  (out of electricity for 6 days).  That last storm cost me about $800 ... $500 deductible when my car got bonked by a branch, not to mention buying storm supplies (batteries, candles, food) and then having to buy all NEW food after my refrigerator slept for 6 days.

NO MAS!!!!!!!!!!!!!!!!!!!!!!!

When will we know for SURE?

BioPat said...

Could be an intersting week.  The storms, this far, have tended west but have managed to stay off the coast.  I would expect no different from this storm's path.  Better to be prepared than not; however I think we'll see mostly rain without the wind factor involved.  I guess this means the early part of winter my be cold but also dry.  No Christmas skil trips for the east coast.

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