Event Discussion-OBS uncertain tracking thread for possible moderate impact event 8A Thu-8A Fri 10/30-31. Mainly 1-3" rains, G 45-55 MPH-mainly coast, and high prob of at least minor coastal flooding - Thursday afternoon high tide cycle.

[wdrag]

Please follow any NWS Watches, warnings, statements that may arise from this coming minor or moderate event.

This is a D4-5 advance heads-up thread for those who have a need to be advised. Modeling has plenty of spread in solutions so that the ensembles are somewhat muted.  There is no doubt in my mind that some sort of minor or possibly moderate impact event is coming. Modeling has been wavering for the past 4 days and hopefully uncertainties resolve by mid week.  If I had plans as a motorist or via air travel Thursday-early Friday, I'd think about delays and how to minimize adverse impact, then possibly implement changes Tuesday or Wednesday  Timing of the 6-10 hour worst case is uncertain. 

Beneficial rainfall should result in October totals at all NWS OKX-Upton climate sites roughly 3.3-4.3", within about 1/2" of normal. Not everyone will get 1"+ but the attached Sunday afternoon 10/26 WPC guidance is a best estimate for D4-5. Rainfall still could end up less than indicated.  A graphic of average return interval (ARI) for various event amounts, at NYC,  is attached-not alarming. 

This could still end up a routine event although I think wind can add impact. Rainfall intensity during one of the rush hours combined with potential for a period of east-southeast wind gusts 45-55 mph on the remaining wet fully leaved trees may result in a scattering of broken limb caused power outages, similar to the 10/12-13 event.

Lunar cycle argues for maximum worst case coastal flooding in the minor category. Modeling from P-Surge is attached.  It might be too robust (follow NWS), suggesting a worst cause 3 ft surge along parts of the coasts during the Thursday afternoon-evening high tide cycle (using Sandy Hook as example).  Lowered pressure this time compared to 10/12-13 contributes to the surge. Please be aware ensembles are not showing much more than 50-55knot se inflow here, limiting potential for excessive rainfall and surge.  

There is a slightest chance for isolated severe however CAPE seems to be very limited, despite the favorable strong shear and diffluent upper level flow.

A 100-150M 12 hour 500 MB Height Fall Center circles northeastward from the southeast central USA into PA/NJ early Friday.  That helps drive the relatively short duration heavy rain event. Presuming the upper Low continues to evolve northward through PA into NYS the eastern Great Lakes there should be a progressive rapid improvement sometime Friday morning.

Westerly winds may gust 25-35 MPH at times during Halloween evening but hopefully without any showers in the area. 

Ensemble rainfall from several modeling centers has been attached as something to look back upon Saturday 11/1 when all the totals are in.  The 500MB ensembles attached also show the 12 hr HFC.  Fairly modest in comparison to some of the operational cycles we've been seeing the past several days.  

If the 5h ensemble pattern prevails or is further west, then we've tracked a routine event. 

The thread current headline will eventually update if moderate impact potential decreases.  For now this hopefully adequately summarizes what is on the table for rain/wind/coastal concerns.

Let's see if its worth tracking. 620P/26

[psv88]

Thanks Walt, great write up 

[wdrag]

Update through 658A/27... no changes. Ensemble modeling continues similar with two groups..eastward wetter GEFS suites and slightly westward EC suites. Results are similar. 

I am not planning to work outside Thursday in northwest NJ, cleaning my gutters of leaves the day before-Wed AM... might need standby DVD in case of internet-power outage Thu afternoon as all modeled products this morning are similar to what we saw yesterday, including the high likelihood of coastal flooding with the Thu aftn-evening high tide cycle.

06z GFS went a little ballistic on qpf and that is related to the nearly stand still Thu aft-evening inflow pattern with PW over 1.5", caused by a suddenly intensifying 5H HFC across NJ---I cant figure the reasons for that... almost like a breathing 5H low HFC... 200M HFC TN Valley a day or two before, then weakens across VA and suddenly strengthens PA/NJ Thurs.   IF it happens, I'd have to add an inland flooding tag to the thread and update ARI since this sole GFS cycle has spot 6" amounts in se NYS.  I'm not buying that solution right now.

One thread change that I may have to make is beef up the chance of iso svr ... but will wait til Tuesday evening before any adjusting.