A beautiful weekend in between hot weather and tropical downpours . . . a signal for the future?
Weather freak Jeff Merz of South Dennis measured 2.65 inches of rain Friday, July 8, into Saturday, July 9. Of that, more than an inch fell in 45 minutes in a Friday morning thunderstorm. This is the heaviest rain since April 12-13, 2011. In Barnstable, Jim Preston of The Cape Cod Time snapped this photo (see the Times story here):
This is the heaviest rainstorm on Cape Cod since the April 13th Upper Low, with training rainfall of 5.9 inches on Martha's Vineyard. The difference between the two storms? In April, we had a slow moving Cold Upper Low over New England. This time, we had a tropical plume of moisture running from The Bahamas into a front from Canada that stalled along the New England south coast. In both cases, a weak (~1007 mb) low moved from Long Island to Nantucket. Also in both cases, we saw an interaction of weather from the north and weather from the south. That is the great part of forecasting weather here in New England. This is also the subject of a discussion I am giving at The National Seashore Visitor Center in Eastham this Tuesday, July 12. Titled "Why Cape Cod has The Most Interesting Weather on Earth", the talk is part of the 50th Anniversary of The Cape Cod National Seashore.
Another batch of that record heat (114^ Medicine Lodge KS yesterday) is blowing into New England on Monday and Tuesday. Then a one/two punch of new fresh air from Canada, just like the fine air here this weekend, will return Wednesday into the rest of the week. Of course with such dramatic changes in air will come wind, lightening, hail, and rain in the period Monday night through Wednesday morning. Some of the storms will contain damaging wind and possible flash flooding. But it's a tough forecast, as we have a prefrontal trough early Tuesday and then the cold front Tuesday night. This may separate the energy enough to have only scattered storms instead of a solid single squall line. So no need to cancel any plans, just be ready for a rain delay or two.
Dry winds will bring great low humidity and sunshine late Wednesday into Friday, followed by a warmup next weekend.
That Cape Cod rain may be a signal of future tropical trouble. That path from the Bahamas to Cape Cod may be repeated later this summer, when the more powerful tropical systems of August and September start showing.