Monday, October 22, 2012

Sandy Forms, Still A Lot Of Model Variance

Tropical Storm Sandy was declared at 5 PM this afternoon as hurricane hunter aircraft found winds at 40 mph. The storm has a pretty low surface pressure already for a low end tropical storm (below 1000 mb) and will have about 48-72 hours of strengthening in the Caribbean.

Sandy has a pretty good shot at becoming a hurricane before crossing Cuba on Wednesday night and Thursday, moving north and northeast at some point tomorrow as the ridge of high pressure to the north of Sandy begins to break down. From there, Sandy's future is highly, highly uncertain and a litany of scenarios are on the table.  The two biggest computer models -- GFS and Euro -- have a spread of over 500 miles for next Wednesday, with the GFS the weaker and east scenario and the Euro a scenario that brings Sandy across New England as a powerhouse nor'easter next Wednesday.

The Euro scenario from today is farther east than the scenario painted last night and outlined in our post earlier today.  This scenario still hammers the whole of the East Coast pretty good but puts the "worst of worst" over New England instead of New Jersey.  Given it's still a number of days out on the model from potential reality -- our thinking is early next week IF (a big IF) it verifies -- there will be a ton of things that can change between now and the final destination.

Most of the hurricane models follow the GFS lead -- which is not a surprise since they are calibrated in part on GFS' data.   Of course, the Euro is in relative lockstep still with the Canadian computer model, which also shows a rather anomalous solution similar to its last three model runs.

Such a strong scenario (944 mb is high end Category 3) is rather unlikely at this latitude, as is the Euro's 935 mb scenario south of Cape Cod.   Those type of scenarios are extreme outliers compared to something like Ida, which was still pretty bad for the Jersey Shore.  Ida was only around 992-993 mb at its strongest as a nontropical coastal storm but because of a strong high to its north it created a tremendous onshore flow and was quite the coastal storm despite a low pressure center that wasn't terribly strong.

A scenario like Ida, perhaps a little stronger, would be a significant issue on the East Coast if it were to play out...however, any of these extreme bombs look may good on paper and a computer algorithm but meteorologically are very tough to pull off and as such should be taken with large grains of salt.

However, Sandy will have to be monitored over the coming days as the models sort out the timing of the approaching trough, the strength of a Central Atlantic low, and the strength of a ridge that builds over Newfoundland.  All of these will factor in how Sandy behaves this weekend and whether it follows a GFS track, a Canadian or Euro track, or does something in between.