Cristobal is the 3rd named tropical cyclone of the Atlantic hurricane season. Strengthening is forecast by The National Hurricane center as Cristobal moves northward away from The Bahamas Sunday Night and Monday. Predicting the strength & path of tropical cyclones is one of the most challenging tasks for meteorologists. Tropical cyclones redistribute heat from the tropics toward the poles, often pulling cold air from the poles toward the tropics on their backsides. It’s weather being weather, the constant thermodynamic balancing due to differential heating of the earth’s surface by the sun. But where and when does it make it’s move out of the tropics toward higher latitudes? It depends on configuration of the jet stream at higher latitudes.
The weather map Sunday August 24, 2014 features high amplitude flow throughout the northern hemisphere. That means deep undulations of cold troughs and warm ridges. Very hot weather and very cold weather. Saturday night in Ireland featured the coldest August night on record. snow fell in Montana and Wyoming. The temperature hit 100 degrees in Savannah Georgia and Springfield Missouri. The high amplitude flow circles the entire globe. As tropical cyclones start veering northward, they can move west or east depending on where the cyclone lies in relation to the trough/ridge configuration. It just so happens that Cristobal is entering a weakness in the pattern between a central Atlantic ridge and eastern North America trough. This likely steers the cyclone toward Bermuda and then accelerates Cristobal out into the north Atlantic. If Cristobal had been a bit slower to arrive in The Bahamas we may have seen more of a ridge on the east coast allowing Cristobal to track west toward Florida and up the east coast with the next trough (the one that caused snow in Montana) arriving on the east coast mid week. Talk about the cosmic tumblers.. Motions in the atmosphere in the North Pacific influence that track of a cyclone in the Central Atlantic, it’s all connected. We just had the anniversary of hurricane Bob, a storm that formed neat The Bahamas in August 1991 and struck New England on the 19th. Cristobal should miss us by 100s of miles on Thursday. Hopefully we get a 5 foot groundswell to surf on by Thursday or Friday.
Here is the forecast from The National Hurricane Center.
In the meantime our New England weather is warming thanks to brief warm ridging on the east coast, ahead of the trough that arrives on Wednesday. This should result in a few of the warmest days of the entire month of August. During the period August 13-24 Boston only warmed to 80 once. We have a shot at 90 on Wednesday. In fact we have already broken one high temperature record, 88 in Caribou Sunday the 24th broke the daily record high of 86 set in 1980. This is rather extraordinary because the high pressure over New England this weekend backed all the way from Greenland where it was full of cold air last week. This has been the summer of extreme blocking for summer time (that means contorted, slow moving, and buckling, jet stream). The blocking high is so strong, a backdoor cold front is being pushed southwest (from Greenland) all the way to Louisiana!
What is the forecast for Labor Day weekend? Great question, most of the guidance has been indicating a high amplitude trough on the east Coast next weekend, which would have featured a stalled front with potential for rainy, and perhaps chilly, weather for next weekend.
But all of the sudden we see a shift with ridging forecast in the east, perhaps because the weather models now are seeing Cristobal pulling the previously forecast trough out into the Atlantic Ocean. I have low confidence in the weekend forecast. Matt, Joe, and Nelly can build a higher confidence forecast for us, by Wednesday we should have a good handle, if not sooner.