Wednesday, August 7, 2024

Wednesday Evening Vermont Debby/Flood Outlook. Still Reasons To Worry

This afternoon's forecast track for what will then be
former Tropical Storm Debby has it centered right
over Burlington, Vermont at 2 am. Saturday. 
 The forecast trends on how Vermont fares with possible flooding from Tropical Storm Debby's anticipated remnants remain roughly the same. 

There's still plenty of cause for worry, and a few reasons for a bit of cautious optimism in some parts of the state. 

Maybe. 

CHAMBER OF COMMERCE APPROVED

Before we get into that, we should revel in what has been a rare for this summer Chamber of Commerce day we had in Vermont today. 

It was beautifully sunny, of course, with a scattering of fluffy clouds to make it all pretty. The sky was true blue, lacking the wildfire smoke that has been hazing up the atmosphere lately. Temperatures were totally comfortable, with highs in the 70s to around 80 in the warmest spots

Humidity was at rock bottom. If the dew point is in the 50s, that's regarding as comfortable. Dew points this afternoon across Vermont were in the  40s to near 50. Just delightful. 

Tonight will be clear and comfortable. Throw open those windows and let the fresh, cool air reinvigorate you and the air in your house. 

VERMONT DEBBY UPDATES

Now back to our regular Summer of '24 doom and gloom 

That westward trend in the forecasts for the expected path of Debby has stopped, and it is still forecast to go right over Vermont.  (Results may vary, it can still go a little west or a little east of us).

For what it's worth, the latest forecast from the National Hurricane Center puts what will then be former Tropical Storm Debby right smack dab over Burlington, Vermont at 2 a.m. Saturday.

This would still mean the heaviest rain might end up falling up in northwest Vermont and New York. That's not cast in stone, however. We still need to worry about possible flooding in many other parts of the Green Mountain State. 

Tropical Storm Debby, just off the coast of South
Carolina when this satellite photo was taken late
Wednesday afternoon, looks kind of 
disheveled, which is good if you don't want
a powerhouse tropical system menacing the East Coast.

The National Weather Service in South Burlington is holding off just a little while longer while meteorologists there await the latest guidance on whether and where to post flood watches. 

I would rate the chances of seeing a flood watch in at least parts of Vermont appear by tomorrow morning.

With Debby going overhead or just to our west, you'll notice the high humidity surge back in tomorrow night as the first wave of rain arrives. 

 The rain Thursday night will mostly serve to wet everything down pretty good. That's what will help set the stage for the flood potential. 

The westward path might allow breaks in the clouds to form during the day Friday. 

That could well only encourage more torrential thunderstorms to eventually break out, adding to a potential flash flood threat. Thunderstorms near tropical systems often have incredible rainfall rates. 

Often four inches per hour. Luckily none of those torrential storms will last anywhere close to an hour in any one place. But they'll still carry flash flood risks. Especially if a couple or few hit the same spot.

Friday will be a humid, unsettled, tropical day to say the least. 

A tropical storm or former tropical storm passing to the west of Vermont can create some gusty south or southeast winds, much like a winter storm passing to our west can cause those damaging downslope winds. 

I don't expect anything super damaging out of this, as Debby isn't - and won't be - and especially powerful system. But with wet ground, some trees could be prone to uprooting in gusty winds. Nothing widespread, and not nearly as big a threat as the possible floods, but it's something to keep in mind. 

Also - and this isn't in any official forecasts I've seen - the east side of tropical and former tropical systems, once they're inland, can produce tornadoes.  It will be interesting if we get the right conditions for a quick spinup with Debby.  I'll wait for further forecasts to see if that low but non-zero risk indeed develops. 

The heaviest rain looks to come through Friday night, so at this point I'd say the period from late Friday afternoon through Saturday morning is the most likely time to see flooding if we get it. 

Current forecasts give most of Vermont at least one to three inches of rain out of this, with locally higher amounts. 

If the predictions for somewhat lighter rain in eastern Vermont pan out, that's good for two reasons. The first is the soils in the Northeast Kingdom are sopping wet, and a couple sunny days before the storm won't cure that.  

So if less rain falls, that might minimize the flood risk. Again, maybe. IF the heaviest rain stays west. For what it's worth, some models I've seen show a slug or band of very heavy rain moving through north central and northeast Vermont overnight Friday and early Saturday, so those areas are NOT out of the woods yet. 

Another reason to hope the heaviest rain stays west would be to prevent torrents from falling in the headwaters of the Winooski, Lamoille and Mad Rivers.  It would lessen the chance of those waterways going over their banks again 

VAGUE OPTIMISM

My guard is still way up with this storm. I still definitely worry Debby could cause another huge mess in Vermont. But that scenario is still not guaranteed,. If there's no guarantee, there's a little hope 

One reason for a tiny smidge of optimism is Tropical Storm Debby, just off the South Carolina coast late this afternoon, is less organized than some forecasts indicated. So its remnants might be a bit less intense than they otherwise would be.

Debby's remnants will race through here much faster than forecasts were indicating a couple days ago. That gives it less time to dump bucket loads of rain on us.,

The system is now expected to move so fast that we have a shot at a Saturday with fairly decent weather. 

As for whether Vermont suffers big time again, or manages to dodge another bullet, we really won't know until this hits. 

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