First of all, don't let the name I've given this rain event scare you...there will be no significant wind like a true tropical system. I just wanted to point out the "tropical connection" this low pressure center will have; and by tomorrow afternoon, when it's pouring, you will understand exactly what I mean.
Today: Many of us will remain mostly sunny through the afternoon with extremely low dew points making for a crisp feeling to the air. (I got some emails from alarmed Mainers wondering if summer was "ova". Don't worry, it's just a temporary lapse into a fall...don't put away that itty-bitty-poka-dot bikini yet.). However, southern and coastal sections of the state will start to cloud up as a low cloud deck rotates in from the ocean. Highs will stay around 70-74 F in most spots, maybe a bit warmer to the west. A late afternoon sprinkle can't be ruled out over York and Cumberland counties, but I'd put it in the 10% chance range. No big.
Tonight: Clouds will thicken rapidly overnight and some light rain/drizzle will develop over southern coastal Maine by 11 PM. The rest of the state will see rain develop in the early morning hours from east to west. (The orientation of the rain shield will be much like a Nor'easter as this low pressure system will be "backing in" from the ocean). The mountains and northern Maine probably won't get into the rain activity until Friday due to the dry air at the surface fighting off the initial bands of precipitation.
Friday: Ok so about this "hybrid tropical" thing. Basically this low pressure system is being spawned from a stationary front that dips all the way into the Gulf of Mexico. As a result it is able to transport that deep moisture into Maine in the form of heavy rain. The heaviest bands of precipitation will set up along the coastline where it will be raining almost all day with very heavy downpours embedded in generally moderate rainfall rates. By the afternoon the focus of the strongest downpours will shift to the Midcoast and end up over Downeast and northern Maine by 5-7 PM. Total rainfall amounts from this storm will top out in the 3-5" range along the coastline, with amounts more like 1-3" farther west away from the core of the storm. Winds will be a bit frisky as well, blowing up to 25 MPH out of the northeast.
The low will start spinning out of the state on Friday night, so by Saturday morning look for some leftover shower activity over the northern 1/2 of the state, while southern Maine begins clearing out.
The entire state should be dry by midday Saturday, leading to a pleasant afternoon with highs in the mid 70s.
Sunday morning will start off with a good deal of sunshine before clouds increase by noon and showers break out Sunday afternoon with an approaching front. In short, the middle part of the weekend will be nice but it will be bookended by showers.
www.facebook.com/meteorologistkeithcarson (I'll be keeping this page when I go to The Weather Channel next week).