Thursday Morning Sandy Update

Hurricane Sandy rapidly gained strength last and also made a second landfall over Eastern Cuba.  Winds were sustained at 110 MPH and the Barometric Pressure was 957 mb (28.26 in).  So far the forecast is on track.  It will not be until later tonight or tomorrow before the track will lock in.  There is still some divergence from global weather models but they all are capturing the same basic pattern evolution.  The block over the Atlantic will not allow Sandy to escape out to sea without some sort impact in the Northeast. First lets start with the National Hurricane Center forecast and cone of uncertainty.
I added the Blue line (wind and rain impacts) and Red (potential snow event)

The environment in front of Sandy is favorable for strengthening, although it may not be reflected in the maximum wind speed.  Instead it is more likely that Sandy spreads its wind field out several hundred miles.  For a densely populated region like the Mid Atlantic and New England this is not a good thing.  The widespread wind field will send an intense storm surge onshore for several days.  There is also a full moon on Monday which means tides will already be higher regardless of whether Sandy roars in or not (it will in some form).  Here is Sandy are a few satellite images of Sandy.

Sandy can still get better organized.  Once in the Bahama's Sandy will begin to grow  as a storm
IR image.  Sandy has all the energy on its Northern edge to consolidate  
So why is it that this system cannot escape out to sea?  The atmosphere behaves as a fluid.  Imagine a rock in a river.  It "blocks" the water from taking a straight path so the river diverts around the rock (or any barrier).  In this case the atmosphere is blocked by High pressure near Greenland.  The high pressure sets up a large ridge in the Atlantic.  Meanwhile, a strong cold front is marching east from the Midwest.  Sandy is moving to north in between these two systems at the moment.  The block won't move; in fact the latest NAO forecast is negative for the duration of the forecast period.  In a negative NAO high pressure is dominant near Greenland and thus the block will not break down.  So that leaves the cold front to capture Sandy.
Observed and forecast NAO (North Atlantic Oscillation)
The trough digging in the Midwest and Great Lakes is very strong.  This will allow the trough to take a "negative" tilt.  Here is the North American Model 500 mb (mid level of atmosphere pressure decreases with height.  Surface is around 1015 mb).  The blue line indicates the negative tilt.
06/25 NAM 500 mb vorticity map
Sandy is likely to try and turn out to the northeast, but will be caught by this trough and will resume a NW and eventually WNW track.  The question is rapidly becoming not if we get hit, but how bad we get hit.  Since I do not believe Sandy can escape out to sea, the question is whether the storm makes a direct hit on Southern New England or the Mid Atlantic.  I lean towards New England because it will be hard for any system to bend into the Mid Atlantic this big and strong.  Although New York City is a compromise it frightens me to think what a warm tropical system, transitioning to extra-tropical all while interacting with an Arctic front could do to New England and NYC with a direct hit.  I will leave everyone with the HPC 6 day forecast.  After today if the trends hold impact maps and timing will be drawn up.  I'll have a post on tomorrow which I will link here.


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