Unsettled Weather for the Weekend

I've been stopped several times this week by people lamenting the forecast for rain all weekend.  Yes I expect some rain but not a washout.  I wouldn't recommend any camping trips to Northern New England but hold off on cancelling the cookouts and pool parties.  Summer is almost over so don't give up on a weekend so quickly.

General Overview
A strong trough of low pressure is slowly moving through the Great Lakes.  The system is trying to move towards New England but it is going to be forced up and over the ridge in the Western Atlantic Ocean.  Here is the upper level 500 mb chart.
12z NAM 8 am 500 mb vorticity, height (image NCEP)
Temperatures are very fall like in the Midwest.  Going back to 8 am lets see who can spot the cold front.
RTMA 2 m temperatures 8 am (image Weatherbell)
Fairly easy in this case.  As of noon the front has pushed a little further east and south, though not much.
WPC 8 am surface analysis
The water vapor satellite image shows the two major weather players for Southern New England this weekend and early next week.  A large upper level low pressure system is present near Bermuda.  This is forecast to slowly acquire tropical or subtropical characteristics over the next several days.  It may very well be named Erika before the weekend is over.  The cold front that will slowly approach should erode and stall somewhere in SNE this weekend and keep "Erika" out to sea but it may come close enough to enhance rainfall.  It will certainly enhance the surf at the shore so heads up if you plan to be in the water this weekend.
GOES_East water vapor satellite 1115 am (image NOAA)
Friday-Sunday
Precipitation ahead of the cold front works into Western New England before day break.  It has trouble getting into Worcester County during the day, but should have no trouble raining in Northern New England.  Friday night the front reaches Eastern New England where it stalls/begins to dissipate.  Temperatures are in the upper 70s/low 80s.  Lower temperatures where it rains a lot.
WPC surface forecast 8 PM Friday
 The hard part of the forecast is how much rain falls.  The subtropical connection off the coast should enhance the moisture flow into SNE.  We have a trigger to initiate convection (the front).  Locally 1-2"+ will fall.  Saturday appears to be the best day for SNE.  On Sunday Eastern MA, Cape and Islands will be at the highest risk for heavy rain as the low offshore makes its move north.  On Monday the storm will be at its closest point, but another cold front from the west will move to kick it out towards Atlantic Canada.

In summary periods of rain and thunderstorms is likely tomorrow through Monday.  Best chances for Western/Northern New England are Friday and Saturday, Southern New England on Sunday with isolated chances on Saturday.The dew points will be sticky as we are under the influence of a tropical air mass.  Speaking of the tropics...

Hurricane Danny
I had my doubts but the small compact nature of Danny has allowed it to strengthen into the first Hurricane of the 2015 season.  Given the overall tropical environment of the Main Development Region this is impressive.  The storm faces challenges as it heads towards the Caribbean Islands this weekend but so far it has shown it is a resilient tropical cyclone.
Hurricane Danny 11 am advisory (NHC)
 Winds are 75 mph and pressure is 992 mb.  It looks good on satellite
GOES_Floater visible satellite 1245 PM
Another tropical wave behind Danny has the potential to develop in the next 5 days.  By Sunday we could have Danny, Erika, and Fred.  Not bad for a strong El Nino year.

-Zack Green

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