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08/27/2012

A Nice Start to the Work Week and It's Back-to-School for Some!

A Scattered Showers Maybe Later Around the NYC Area, Thunderstorms for Tuesday a Sure Bet!

Good Morning, 

A ridge of high pressure is located off the coast of New England early this morning... And, the

continuous flow of moist air being pumped into the mid-Atlantic states led to some very heavy

rainfall in central and eastern Maryland yesterday... Its ironic, because while the sun was out and

temperatures were in the mid and upper-80s along the I-95 corridor between New York City and

Philadelphia, pockets of heavy rain were occurring less than 100 miles to the south and west...

 

Two observation sites located in the Greater Baltimore Area had over three inches of rain (3.36"

fell at the BWI Airport in Glen Burnie, while 3.37" fell at the Maryland Science Center, located at

Baltimore's Inner Harbor)... We do have a couple of showers and a thunderstorm in the forecast

across eastern Pennsylvania, New Jersey and southeastern New York today and tonight -- if for no

other reason than there'll be some old boundaries of outflow left behind by those earlier showers

and thunderstorms... Assuming that there's at least some sunshine today and decent mixing of

this very moist air mass, it won't take much of a "trigger" to cause a shower or thunderstorm in

some of the other big, coastal cities... Once again, temperatures will be in the mid and upper-80s,

especially if the bulk of these showers and thunderstorms hold off until this afternoon...

 

Tonight and tomorrow, a cool front (which is currently located in the Great Lakes) will be pressing

to the south and east... This will be providing the Northeast and much of the mid-Atlantic region

with an additional focal point of showers and thunderstorms... The various global models vary on

the timing of this front's arrival and eventual passage, and we tend to be leaning more towards the

ECMWF (European), which is the slowest of these... The rationale being applied here is that the

ECMWF has been performing better than the domestic models when it comes to forecasting the

track of "Isaac"... And, since that forecast track has been trending farther and farther WEST with

this tropical cyclone, indicating that its eventual landfall will occur close to New Orleans during

midweek, the assumption is that weather systems which are located 'upstream' (fronts, high

pressure systems, etc.) will be influenced by it... Therefore, we're allowing for a couple of showers

and a thunderstorm tonight and at ANY TIME tomorrow, before the cool front finally manages to

push through the area later tomorrow night... Previous forecast continuity had them occurring

'mostly through midday' before ending... Behind the front, a strong ridge of high pressure will be

building into the Northeast Wednesday, Wednesday night and Thursday...

 

Getting back to "Isaac", the center of circulation managed to pass just to the south of Key West

late yesterday... It is now emerging in the eastern Gulf of Mexico, and it is expected to undergo

steady strengthening while its forward speed also begins to slow down... About five days ago, the

European's model output had been indicating that the future track would be farther west than most

other sources, and it looks as if it is going to outperform them this time... Now that it is moving

away from Florida, the big questions are: "Where is it headed?" and "Just how intense will Isaac

be?"

 

The current thinking is that "Isaac" will be making landfall on Wednesday morning somewhere

along the Central Gulf Coast, probably on the shores of Louisiana or Mississippi... When it does, it

will be a Category One with maximum sustained winds between 75 & 90 miles per hour...

 

The confidence in its intensity is a little less than the track at this time, but it certainly looks like

there will be a profound impact on areas between New Orleans and Mobile, Alabama -- with the

worst effects being felt late tomorrow night and throughout the day on Wednesday...

 

Last evening's 00z run of the European model show the storm's center reaching land somewhere

between Biloxi and Gulfport, Mississippi around daybreak on Wednesday... Assuming this is correct,

there'll be a storm surge of no less than 6 feet and hurricane-force winds ramping up between midnight

and 7 a.m. on Wednesday in these coastal communities...

 

Torrential rain should then spread out across the Southeast, with the Lower Mississippi Valley

probably bearing the brunt of the heaviest rain, exceeding a foot later this week

(mostly inland from late Wednesday or Wednesday night into Friday)... But, because of the high

pressure system acting as a "blocker" to the north, it is doubtful that anyone in the Ohio Valley, the

mid-Atlantic states or the Northeast sees any of this heavy rainfall during the next five or six days...

 

Have a good day!!!

Posted by WABC on August 27, 2012 | Permalink

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