Forecast- T.S. Alberto Mostly Misses Us
By Erica Grow on May 20, 2012, 11:12pm
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The tropical season hasn't officially begun, but already we have a storm in the Atlantic. Tropical Storm Alberto formed on Saturday off the coast of the Carolinas. It's a fairly weak storm right now, with winds of 45mph, and the tropical storm-force winds only extend about 40 miles out from the center of the storm. Upper air analyses show no vertical structure to this storm at the moment- there isn't a closed low of falling heights, and the vorticity map looks no more impressive than a typical summertime MCC. The model progs don't strengthen this storm at all as it begins its northward trek, which makes sense because tropical storms need water temperatures in the upper 70s to near 80 degrees in order to strengthen. Current buoy data shows water temperatures only in the upper 50s near Long Island! Alberto's track is expected to remain offshore, which means the storm won't be able to draw strength from the land/ocean interaction which is a source for energy in a typical Nor'Easter storm.
Alberto is progged to be northeast of Connecticut, out over the open ocean water, by Wednesday. At the same time, GFS shows a cold front moving through, with a disturbance in the jet and a weak line of vorticity. GFS is the most generous with precipitation on Wednesday, though the NAM and Euro both also have minimal QPF values.
After Wednesday, we should dry out-- but today's model runs were showing a new feature. An area of low pressure pushes through the back side of a trough over the Great Lakes region and brings some moisture to Connecticut on Thursday (according to GFS) and on both Thursday and Friday (in the Euro output). The models differ in precipitation because the GFS output keeps the area of low pressure mostly to our south as a closed upper-level low, whereas the Euro shows the low opening up and becoming disorganized on Friday. I'm leaning toward the GFS solution which keeps the low closed and turns it away from us, because the Euro isn't showing a mechanism (like a strong jet) that would rip the low apart.
850mb temperatures rise on all model data as we head into next weekend, back to around +15C by Friday. With an area of high pressure offshore to our east on both GFS and Euro, I expect that humidity levels will rise with an onshore flow. The models differ on the placement of a shallow mid-level trough; the GFS shows the trough moving through with a disturbance on Saturday, whereas the Euro keeps the trough well to our north in Canada. The GFS model shows a line of showers and thunderstorms developing in conjunction with the jetstream disturbance on Saturday, but the Euro keeps us dry all weekend long. Next weekend is Memorial Day, of course, and as of now, it looks like the forecast has a summery feel to it with higher humidity and temperatures 5-10 degrees above normal.
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