Let me be clear, this storm will not be as intense a storm as Sandy and will not be a hurricane. Rather, it will be an extratropical storm driven by horizontal temperature variations. But it will be capable of producing strong (40-50 kt) winds and flow that can push water inland over vulnerable areas. It will me a major storm.
Lets turn first to European Center model, which did so well during Sandy, and which generally has superior verification to the U.S. GFS. Each of these forecast maps show sea level pressure (in hPa or mb) and relative humidity near the surface (2m). At 10 PM PST Wednesday, we find a strong low off of Maryland, with very strong pressure differences (gradient) along the coast. There would be powerful easterly onshore winds across coastal NJ and in LI Sound with this pattern. Central pressure perhaps 978 hPa.
The low is unfortunately slow moving. Twelve hours later (10 PST), the low was off New Jersey, with a central pressure a bit less than 984 hPA. (Remember Sandy was 946 hPa at landfall!).
7PM Thursday the low is just SE of the east end of Long Island.
What about winds? Here are the predictions for near-surface winds at 7 PM Wednesday. Some sustained winds reaching 50 kts, with higher gusts. This is serious stuff. Strong enough to down trees and capable of creating a modest storm surge.
What about the U.S. GFS model? Here is the forecast for Wednesday at 10 AM from the model run started at 5 AM Saturday. Deep low a bit more offshore and faster to move northward than the European model.
This is a major shift for the U.S. GFS model, which had the low way offshore yesterday:
|GFS forecast started 18z Nov 2, 147 hrs (valid Thursday, 1 PM PST)|
As I have noted many times in the past, one should not look only at the high-resolution forecasts, but should study the ensembles to evaluate the uncertainty in the forecast. This figure shows the high resolution European forecast at 4 AM PST Thursday on the right and the MEAN (or average) of the ensembles (many forecasts at somewhat lesser resolution) on the left (both blue lines). The shading in both is a measure of uncertainty. The ensemble mean has a low center that is broader and centered a bit offshore of the high-res prediction. The shows there is some uncertainty in the position and intensity of the low, but clearly most of the ensemble are going for a coastal cyclone.
The ensemble of the GFS models runs, show below (starting and ending at exactly the same times), is very different, with ensemble mean off of New England, with lots of uncertainty to the west.
The issue of the relative skill of the U.S. and European models has garnered a lot of media attention this week, and I will return to this critical subject in a future blog. As a sample, here is a graphic on the NBC nightly news on Friday night (white is the actual path).
I will be giving a talk: Global Warming Over the Pacific Northwest, Separating Facts from Hype, at the Mountaineers in Seattle at 7 PM on Thursday at the Mountaineer's facility in Seattle (Magnuson Park). Open to the public ($5 contribution for non-members). For more information, go here. Will talk about Sandy's implications as well.