The rain is here and it is not going to be stopping any time soon through this weekend, which will be a perfect time to catch up on some movies, a good book, or perhaps finally conquer a very difficult video game. What ever you do this weekend, it likely will not be done outdoors.
Light to moderate rain continues to develop and expand north and west over much of the Philadelphia and New York City metropolitan area. This rainfall is not directly connected to what will be an impressive coastal storm tomorrow morning, but is a result of the developing moisture advection at the mid levels off the Atlantic and a stationary front positioned along the New Jersey coast. The isentropic lifting produced by this frontal boundary is supporting the development of this rainfall, which will have breaks in the steady rain from time to time. However, for this rush hour, steady rain and increasing winds from 15 to 20 mph with gusts over 25 mph can be expected for the New York City metropolitan area down through the northern Philadelphia metropolitan area. More scattered rainfall can be expected further south and west, over the Hudson Valley, and Connecticut.
The upper level dynamics for this storm, namely the 500 MB low over the Mississippi Valley is developing as expected. Note the spreading out of the moisture off the Southeast coast. This is a calling card for divergence aloft and means that lifting will continue to intensify as the evening continues. This fanning out of the moisture plume from the Sub Tropical jet stream has been expanding north and west through the day in response to the Polar jet stream and upper low interacting with the Sub Tropical jet stream and tilting the long wave trough axis into a negative position. Currently, the two jet streams and associated disturbances remain separate, as we can see with the area of dry, sinking air between the two areas of lifting (moisture). However, the development of mid level moisture and weak lifting over central and eastern South and North Carolina means that the phase of the two jet streams is on the way.
When the phase occurs this evening, the primary low over the Tennessee Valley will weaken rapidly and the coastal low over North Carolina will become the new primary low pressure system. Strong upper level divergence at 500 MB on up to 200 MB will support strong lifting throughout the Mid Atlantic and allow the surface low to deepen into a strong coastal storm by tomorrow morning. With the trough tilting into a negative position, the upper, mid, and low level jet streams will all set up in an orientation from southeast to northwest, which will drive plenty of Atlantic moisture right into the northern Mid Atlantic and support a prolonged heavy rainfall event. The final piece of the puzzle is the high pressure system over Quebec (note the dry air seen in black over Maine) that will enhance the pressure gradient and support a strong easterly wind sustained at 20 to 40 mph throughout the region with gusts over 60 mph possible along the coast and over the coastal waters.
Because the upper low captures the surface low on Saturday evening and causes the storm to become vertically stacked, the low pressure system will be slow to exit, which will keep rain in the forecast through at least Monday afternoon. However, the worst conditions are expected on Saturday afternoon through early Sunday morning where very heavy rain will develop and sustained winds will be at their peak.
The rainfall map to the left includes today’s rainfall on through Monday morning, which will be rather impressive for many locations. The potential for over 4 inches of rain is very real and given the mesoscale forcing that will develop due to the stationary front just off the coast, the threat needs to be addressed.
This storm will be capable of flash flooding of rivers, streams, and urban locations throughout the region, thus theFlash Flood Watch that has been issued for the region. Due to the persistent easterly wind, a Coastal Flood Warning, as has been warned about by me for several days, has also been issued for much of the New Jersey coast. High Windand Gale Warnings have also been issued to address the strong winds that are expected. Those that may be boating in these conditions should also take head of the Small Craft Advisory for this weekend that has been issued as well.
The good news is that after this storm, the weather pattern improves significantly with high pressure dominating the northern Mid Atlantic from Tuesday on through next weekend with dry conditions, clear skies, and temperatures in the 50’s and possibly even 60’s for the Delaware River Valley.
So my advise for this weekend is stay home or at least indoors. Hey, at least it’s not snow!
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