An unseasonably warm and humid air mass has built into the region out ahead of a cold front pressing through the Great Lakes. Temperatures over the last few days have been well above normal and dew point values have climbed into the lower 70s. The air feels quite uncomfortable, particularly by mid-October standards!
The arrival of the abnormally humid air is being assisted by tropical moisture streaming northward from Hurricane Michael, which made landfall near Panama City, Florida Wednesday afternoon.
It’s the combination of this warm, muggy air mass, the advancing cold front and tropical moisture lifting up the Eastern Seaboard in association with Michael’s remnants that are poised to give us a shot of some heavy rain later today and tonight.
Expect mostly cloudy skies through the day on Thursday with showers developing across the area this afternoon. As we push into this evening and the first part of tonight, bands of rain will become more numerous over the area, with embedded downpours crossing the Cape. This will represent round one of a two-round rainfall event.
Precipitation is likely to taper down a bit during the overnight hours but a second, more robust, surge of rain will develop late tonight as moisture from Michael gets entrained into a frontal zone draped over the Cape and Islands. It’s during this second window of rain…likely sometime between 3AM and 9AM that very heavy…perhaps torrential at times…downpours will move over parts of the Cape and bring with them pockets of street flooding and basement flooding.
It should be noted that there will be a tight south to north gradient between the heaviest bands of rain and much lighter, more nuisance variety showers. Consequently, the odds for heavier rain are higher on the southern side of the Cape versus the far Outer Cape near Provincetown and Truro.