Monday, 11:45 A.M.
The first month of the Atlantic tropical storm and hurricane season is pretty much in the books, and so far it has been quiet. That may soon be changing, as an area of showers and thunderstorms off the east coast of Florida is beginning to show signs of marginally better organization. A broad area of low pressure appears to be forming, and as it sits and percolates over the warm Gulf Stream waters the next 48 hours, that low should gradually become better and better organize. This could lead to not only the first tropical depression of the season, but the first named storm.
The process of a tropical storm coming together will take some time. Right now there's still a little too much northerly wind shear over the system, so these disorganized showers and thunderstorms are primarily south of what low-level center there is. An upper-level trough of low pressure swinging through the Midwest into the Great Lakes and Ohio Valley tomorrow and tomorrow night will cause those northerly winds over the low off the Florida coast to relax, which should allow the storm to begin to strengthen, probably into a depression. The water temperatures are sufficiently high enough that a feedback process can then develop Wednesday and Wednesday night into Thursday to allow for additional strengthening, and this may then become Arthur.
With this trough digging into the Midwest, look for a strong cold front to make steady progress across the Midwest tonight, and into the Great Lakes and Ohio Valley tomorrow. There will be one more steamy day in the Ohio Valley tomorrow with some sunshine and temperatures not far from 90, while east of the Appalachians, many places should surpass the 90-degree mark with dew point temperatures up near 70.
Look at the 500 mb forecast for Wednesday morning:
You will note the presence of the system east of Florida, as well as the aforementioned upper-level trough, which is really two separate troughs. The first one is already by passing the Great Lakes, and will help pull the initial cold front into upstate New York down into eastern Ohio and Kentucky. The second trough will be swinging through the Midwest behind it, and should eventually push the front farther south and east later Wednesday and Thursday.
That said, with the upper level ridge in place off the East Coast, the upper-level winds will become parallel to the lead front. When you add that in to the fact there will be some sort of tropical feature lurking east of Florida, and you can see why Wednesday will be a hot, steamy day in the East, a day that is likely to spark some strong to severe thunderstorms from upstate New York and western New England down into Virginia later Wednesday to slice into the heat.
It will take this trailing disturbance some time to turn the corner and move across the Ohio and Tennessee Valleys Thursday, so the front will just limp over the Appalachians. Therefore, even Thursday will still be quite warm and humid up and down the Eastern Seaboard. By this time we should have either a strong tropical depression or a named tropical storm moving north, if not north-northeast, toward the eastern North Carolina Coast. It's not certain if it will make landfall, but it if it does, probably sometime Thursday night or Friday morning, the Outer Banks would be the most logical place for that to happen. Keep checking in to AccuWeather.come for the latest internal thinking on this system.
Finally, on Friday, the storm, in whatever form, should begin to accelerate off the northeast, pulling the front off the coast in the process. The day should end with much lower humidity in the East, setting the stage for another gorgeous weekend with no heat and low humidity from the Ohio Valley to the Northeast.
Meanwhile, the places experiencing this chill today and tomorrow into Wednesday will begin warming over the holiday weekend, as the upper-level trough lifts out, and another upper-level ridge of high pressure returns to the western Plains and eastern Rockies. Here's the GFS 500 mb forecast for Saturday evening:
This will lead to a warm weekend over the western and northern Plains and Rockies:
One can expect the heat to move into the East sometime next week.
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