After dry, albeit mainly cloudy skies for New England under high pressure, the region's next system will be moving in after midweek amid a relatively interesting setup. This will come as what will soon be Hurricane Helene bears down on the southeast. While this storm won't directly affect New England, the weather is one big machine and everything is connected in some way.
For today and Wednesday, a trough will remain to New England's west as high pressure holds its ground over New England. This system will likely cut off from the main flow and drift toward the Mississippi River Valley on Wednesday. This will help keep most of New England dry for the day, although some fringe showers may drift well inland across western areas during the day.
Heading into Wednesday night and Thursday, the surface low pressure (shown above over Michigan) will move northeast and run to the north of New England. This will come as a northern stream trough dives southeastward from Canada due to strong ridging near Greenland. All of this is to say that a plume of rainfall will move through New England Wednesday night into Thursday. These showers will move generally from west to east during this time.
The rainfall may come in two general batches as the system drags its fronts across the region. The first would come as the system's warm front brings more moist air into the region followed by somewhat of a break and a second round of widespread showers associated with the cold front. The best chance for a longer period of steadier rain and higher rainfall amounts will be across northern New England, closer to the center of the low.
As of now, a general quarter inch to an inch of rain is looking rather widespread across New England. Higher amounts will be more likely across northern New England with lesser amounts the farther south you go. Overall, rainfall amounts may end up varied with some areas seeing heavier downpours while others may dodge them.
Current Weather Prediction Center rainfall forecast through Friday morning:
While all of this is going on in the northeast, what will soon be Hurricane Helene will be approaching the Florida Panhandle as a major hurricane. This storm will likely make landfall in the southeast around Thursday evening, potentially as a category three hurricane. This will bring a major rainfall event for the southeast (you can see the current forecast above) as well as typical hurricane impacts with very strong wind and a powerful storm surge.
As we said in the beginning, the weather is a machine and all of it is connected in some way. Initially, the system moving into New England for Wednesday and Thursday was looking to bring the most rainfall to southern and/or coastal New England. However, the cut off trough over the Mississippi River Valley will now remain to the south and interact with the hurricane rather than slide eastward. The higher rainfall trended north into northern New England as a result as the center of the low pressure system will slide to the north of New England.
Image below: 500mb height anomaly map (which shows blue troughs and red ridges) for Thursday afternoon. This gives a good visual for what is written above:
After this system moves through New England, high pressure looks to rebuild over the region on Friday afternoon and heading into the weekend. The overall setup once the system passes is looking very similar to what occurred a few weeks ago with the remnants of Hurricane Francine. That is to say that the high pressure over New England will keep the remnants of Helene in the southern and central United States. The storm will likely wither away over the south through the weekend while New England dries out.
Current weather map for Saturday (September 28) showing low pressure still over the Mississippi Valley with high pressure building over New England:
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