Rain coming Wednesday, but how much depends on path of coastal storm

By Terry Eliasen, Meteorologist, WBZ-TV Exec. Weather Producer

BOSTON — The WBZ Weather team is issuing a NEXT Weather Alert for Wednesday. This is a highly unusual storm system for the time of year and weather models are having a heck of a time pinning down the track.  You just don’t see many coastal storms in August, unless they have tropical origins.  

Why? These storms need a source of energy to gain their strength. Typically, that comes from the contrast of air masses (cold vs warm) or the difference between the warm Ocean and colder land. This setup is seen much more often in Fall and Winter, certainly not in mid-August when, essentially, it is generally warm everywhere (water and land). So, the formation of this coastal storm off the Carolinas and its subsequent trek northward has forecasters and weather computers befuddled. What do we make of this thing?  Where is it going? Some models are blowing it up like a classic nor’easter, complete with copious amounts of wind and rain.  Others give it a “meh”, sending it rather harmlessly to our east and up towards Nove Scotia.

Clearly, if this were wintertime, the stakes would be enormous. We’re talking a couple feet of snow versus a partly sunny day. I would argue that while this storm won’t be nearly as impactful as a wintertime nor’easter, the stakes are still quite high given our recent drought and the need for rain. A couple inches of water would be one heck of a start towards replenishing our water supply.

So…What’s the deal?

It appears as though both of the most dramatic scenarios are now unlikely. The chances of both a complete miss and a total, region-wide drenching are lessening. The most likely scenario is something right smack in the middle. A track close enough for SOME impacts (mainly near the Coast), but not close enough to raise any major concerns or put any real dent in our drought. The areas at most risk of heavy rainfall are…

• Extreme southeastern MA, especially Cape Cod and the Islands
• Coastal Essex county, including Cape Ann
• Coastal New Hampshire & Maine

TIMELINE:

The first rain bands came ashore over Nantucket as of Tuesday afternoon. This initial burst of rain will slowly push northwestward over most of Cape Cod through Tuesday evening.

The rain becomes steadier and heavier later, mainly early Wednesday across southeastern MA.

By dawn on Wednesday, there should be rain of varying intensity across most of eastern MA, but again, the heaviest is likely to remain down towards the Cape and Islands.

During the day Wednesday, we expect the off and on showers to continue across eastern MA, the farther west you go, the drier it gets. We don’t expect much rain at all in central and western MA.

Later Wednesday and into Thursday morning, the focus shifts northward into Maine and parts of New Hampshire. The storm gets a second wind up in the Gulf of Maine and is likely to bring a few inches of water to parts of Coastal Maine. There may be a band or two of rain that pinwheels southward as far as the MA/NH border very early on Thursday.

By Thursday afternoon, the storm is pulling away and we are left with just a few scattered, very light showers in central and northern New England…sunshine emerging to the south.

RAIN AMOUNTS:

Best chance of seeing an inch or more: far southeastern MA, including the outer Cape and Nantucket…but more so coastal New Hampshire through the entire Maine coastline…also possible along coastal Essex County in MA.

Decent shot at seeing a half inch: areas east of 495 including a good portion of Middlesex County, all of Essex County, Suffolk County, and Plymouth County…also most of Hillsboro county in New Hampshire. 

Less than a half inch: west of 495…Worcester County, Bristol County

WIND:

This will not be a major wind event, however, there will be some gusty northerly winds over Cape Cod and the Islands as well as over outer Cape Ann. During the day on Wednesday, we expect maximum wind gusts between 30-45 mph from Cape Ann to Cape Cod. For the rest of the area we don’t anticipate the wind being much of a factor, perhaps gusting 20-30 mph here and there.

THE SEAS:

There is a high surf advisory and small craft advisory in effect for Wednesday as seas between 4-8 feet are expected.

Stay tuned to WBZ-TV, CBSBoston.com and CBS News Boston for updates throughout the storm on Wednesday.