Tropical Storm & Cutoff Low Battle Looms
Tropical Storm & Cutoff Low Battle Looms
Rain Late Week From Non Tropical Low Along East Coast
Could Provide Drought Relief For Dry Areas
Tropical System In Caribbean Complicates Long Range Outlook
The week ahead forecast is going to be challenging to say the least. We not only have to deal with a “cutoff” low that might bring us a prolonged widespread rain over a period of several days but we also have the complication of a possible tropical storm in the Caribbean. That cutoff low is going to be the key and the driver of events this week and with the tropical system next weekend.
The first thing we should do is explain what a cutoff low is. A cutoff low is a strong (or weak) low pressure area in the upper layers of the atmosphere that is separated or “cut off” from the main jet stream flow that would otherwise move weather systems along from west to east. Cutoffs alter the jet stream pattern as shown above. The East Coast cut off low creates a huge weakness in the upper flow from the Middle Atlantic Coast southward into the Caribbean. In this particular case that weakness is where a possible tropical storm would gravitate to and turn northward rather than continue to move westward.
We should point out that said tropical storm has not even formed yet but all weather models are developing this system over the next several days in the Eastern Caribbean and moving it west northwestward toward Cuba. But let us lay that aside for the moment.
Back to the cutoff low. This system dives southeastward from the Great Lakes toward the Middle Atlantic Coast creating low pressure just offshore. There is a large high to the northeast creating a strong onshore flow and good inflow. This would mean rain beginning Wednesday night (after the rain we get Monday night into Tuesday) and that rain will continue on and off until the weekend or until the cutoff low either weakens or pulls away to the northeast.
We are still getting rain from this into Saturday where at this point the upper air cutoff low is pulling out to the northeast. Now here lies the problem with any tropical system. Is the weakness left behind in the upper atmosphere enough for any tropical system to move northward. The GFS says it is.
The GFS model opens the door for a more northerly track of any tropical system around the western side of the big atlantic ridge. Think of these weather systems essentially like railroad tracks where the tracks constantly are subject to change. You can see the alley way that is created at this moment in time. But these things don’t stay the same for too long.
The GFS continues to shift this system eastward over the last few days because of the influence of the cutoff low that creates the weakness. The next key will be the trough approaching from the west. It has a broad look to it which would favor an offshore north northeast track versus a more northerly track. This is going to be another variable to consider in the longer term. Given all the uncertainty in the models, and given the huge volatility of weather models in general recently, the wise approach is to at this point watch and wait. First off we have to see if this tropical storm does develop. The National Hurricane Center in its latest forecast rates this system with an 90 percent chance of developing into a tropical cyclone. In fact latest satellite pictures indicate that the system is already beginning to organize.
Meanwhile back to the cutoff low for late this week. It could be a substantial rain producer. The GFS rainfall forecast map through Sunday shows total weekly rainfall of 3 inches or more in many places.
First things first is the question of the system along the east coast this week. That issue must be resolved first. Among other things, if the cutoff moves out faster, it would create a more westward track in the Caribbean by delaying any northward turn. The other possibility is that the cutoff takes longer and longer to pull out and creates such a sustained weakness, that any tropical storm turns sooner and passes well offshore. There are way to many variables here at this point to even begin speculating beyond the work week. The good news could be that this lead system could put a substantial dent in the severe drought conditions over many parts of our area.
Of course this is only one model’s view. The European will have something to say about this and we will examine that model as well in a separate post later this evening.
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