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Another big Sept rain event between roughly midnight Friday morning and midnight Sunday morning (bulk 9/29-30/2023)


wdrag
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Periods of rain, some of it heavy at times is destined for most of the NYC subforum Friday-Saturday as low pressure develops off the mid Atlantic coast into a vertically deep slow moving cyclone. PW increases at times to near 1.7" in warm advection along the inverted trough Friday then the pinwheeling PWAT circles back around our area Saturday. Gusty northeast-east winds  Friday morning to 35 MPH and the constancy of northeast flow this week at the time of the highest tides in Sept should yield at least minor coastal Flooding within 2 hours of high tides Friday and possibly moderate coastal flooding at the highest tide cycle Saturday or Sunday as the backwash of the offshore storm shoots some 45 MPH north-northeast winds down the NJ coast by Sunday morning. 

The previous 3-4 day rains are attached, and the numbers for this coming one may exceed 6" again in parts of the NYC subforum.  If so, where?   It's possible, despite all this projected rain, that flooding might be imited to a few small areas. Too early to be sure as of 447PM/27.

The EPS has been most aggressive with this system since 9/24 cycles and the 12z/27 EPS mean rainfall is attached.  These values are quite high and much higher than the GEFS 12z/27 cycle with the GEPS midway between.  If it causes fresh water flooding---where?  Not sure this will be very much freshwater flooding except possibly NJ/CT/urban LI. 

This topic should serve also for the rainfall reports.

 

at 505PM added the tag power outages.  If this rainfall develops per the more aggressive 12z/27 EPS mean, rain softened ground from this past weekend combined with new 2+" rainfall may allow spotty power outages due to tree uproots of still fully leaved trees. 

Screen Shot 2023-09-27 at 3.31.41 PM.png

Screen Shot 2023-09-27 at 3.39.24 PM.png

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Friday is concerning... persistent onshore flow leading to massive FGEN banding. as the banding pivots, it appears there is the potential for 2-4" amounts or greater, but who knows where the banding will set up. it's similar to a Norlun in that regard

classic sloped FGEN with potent 700mb omega. kinda similar to something you'd see in the winter

ENS and mesos are in agreement, and given the lead time of only two days, it appears like a significant flooding event is gaining traction

image.thumb.png.0dfd94365cdef19694ff95f9081be0f0.png

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1 minute ago, brooklynwx99 said:

Friday is concerning... persistent onshore flow leading to massive FGEN banding. as the banding pivots, it appears there is the potential for 2-4" amounts or greater, but who knows where the banding will set up. it's similar to a Norlun in that regard

classic sloped FGEN with potent 700mb omega. kinda similar to something you'd see in the winter

ENS and mesos are in agreement, and given the lead time of only two days, it appears like a significant flooding event is gaining traction

image.thumb.png.0dfd94365cdef19694ff95f9081be0f0.png

Yep the only question is where. Rgem is focused further east than the nams and hrrr

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Upton not impressed

&& .HYDROLOGY... Rainfall from Thu night into Sat somewhat uncertain. Areas from NYC north/west and across SE CT/eastern Long Island appear most likely to see at least 1-1.5 inches. A stronger offshore trough/low could Fri into Sat could result in heavier rain of over 2 inches for parts of SE CT/eastern Long Island. Duration of this rainfall should limit any hydrologic impact.

 

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29 minutes ago, winterwarlock said:

Mt holly doesn't  seem bullish as they are forecasting  just half inch to inch

I think our WFO's tend to stay close to WPC beyond 12 hours... one NWS voice. They also had the conservative GEFS on their low side.  Just saw the 18z EC OP... continues bullish-attached.  Uncertainty with RRFS/NAM tending more NYS or west of NYC, while EC is definitely east of RRFS.  Time to iron this out and also figure the confidence of seeing any 6's.

 

NWS Blend of Models also much less than EC/EPS, GEPS, RRFS/NAM. 

Waltimage.thumb.png.70879b2521883e78cc3a19348710b273.png

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I'll add my 2c at 5P...  suggest mowing completed today. You may not like your soggy ground even on a rain free Sunday I84 corridor southward NJ-seNYS-SNE-LI. My guess is that NWS is waiting on any FFA because the GEFS/SREF/NAEFS are much more conservative than the GEPS-EPS 2-4" event and as you've all posted the iso 7" on highly resolved mesoscale guidance.  Also, NWS may be holding off due to no ensemble guidance showing minor flooding which is because these river forecasts use the ensemble output which seems to me wayyy too low. 

 

More at 5P after mowing.

 

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