Weekend Nor'Easter Update # 4: Heavy Rain, Wind & Flooding Unavoidable

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It really feels as though forecasting these events goes on forever and ever! They seem to drag on... maybe because with today's technology we can actually pick up on these events nearly 2 weeks in advance. The general issue is the fact that even when they can be detected so far in advance, the forecasts change many times before the actual event impacts the region. That is why I'm SO against putting details out beyond 4-5 days out. Let me give you an example: I'll concede the GFS, which I often poke fun at, DOES DO a good job picking these things out, HOWEVER it is going to miss the mark in a big way on intensity. 7 days ago it had a major 967mb low impacted our region. In reality? Our low will probably be just under 1000mb. Quite the difference. That model run prompted several social media forecasters to go into armageddon mode and make ridiculous comparisons to stronger storms like Sandy. That is why I say social media is a gift and a curse. It's a gift because I can instantly connect with thousands of people and get my message out but it's a curse because I'm constantly battling mis-information.

GFS 7 days ago:

Current GFS:

Big difference... hardly a historic storm as was being pushed out there by many...

Anyway, where are we and where are we going? There's no getting away from this one. It's going to rain, we ARE going to get some strong winds and there WILL be some tidal flooding. There's no chance it's going to just head out to sea. Why? We've got "blocking" to the northeast. High pressure will prevent an out to sea option due to the north atlantic oscillation (NAO) going into its negative phase... this is what that looks like. Note the storm track bucking back towards the coast:

The NAO in its negative phase also helps slow storms down and stops them from being progressive. For this reason we will see the on-shore flow pick up by Friday night and be with us for a good 12-18 hours with the heaviest winds here for perhaps 12 hours in total. Our nor'easter is going to creep up the coast. 

Alright let's get down to brass tacks and dive into the details:

TIMING: 

Cloudy skies begin to build by late Friday morning, the leading edge of rain will be down to our southwest towards Baltimore and DC around 4pm. I think showers will arrive in our backyards by dinner. 6-8pm with the intensity picking up the later we go. The heaviest rain will actually fall overnight into very early Saturday morning. The worst winds will be 2am-10am. The low should be right over us by Saturday afternoon and if it takes that track we will likely "dry slot" meaning there will be an area of dry weather as the rain pushes north.

RAIN:

1-2" seems reasonable. We certainly do NOT need the extra rain. I think given the track of the low either on top of us or slightly east, there will be a WIDESPREAD area of 1-2". Rain will be with us through probably early afternoon at the latest (the most organized that is), some lingering showers possible but I don't foresee the rain lasting ALL day. Forecast rain totals:

WINDS:

Winds will be light early Friday but begin to pick up out of the southeast and then east and northeast as we go into late Friday. I'd say after 10pm we'll see sustained winds slowly increase to 20-25mph with gusts over 40mph region-wide given the track of the low and it's close proximity to our region. It's relatively uncommon that the strong winds are universal. Wind Gust Forecast:

Some of you (who may be fellow weather geeks) may be looking at the model guidance and see the low is going to be around 1000mb. You're probably asking "How can we get just strong winds?" It's all about the PRESSURE GRADIENT. Strong high pressure to the north will allow constriction of the isobars and that's what will make winds really pick up. 

 

FLOODING:

There are 3 tide cycles we need to watch closely. Friday night, Saturday morning and Saturday night. The worst will be Saturday morning as it's the highest tide this weekend. Being just 3 days removed from the full moon our tides are astronomically high, they're running about 1-1.5' above the norm. Add in a persistent wind and the potential for "stacking" of the back bays? I think moderate flooding is possible, especially through Cape May county. My concern is the wind preventing all the water from the Friday evening high tide from draining. This would make the Sat AM tide even higher. With the low traveling over our region, the pressure drop could keep the tides higher for the evening tide. 

Here's a look at the predicted tide heights for Cape May. Notice several rounds of at-least minor... I think we will see moderate, especially Saturday AM.

SUMMARY:

3 out of 5 for impact. Heavy rain, high winds. Winds should relax later in the day and rain shuts down through the morning / early afternoon. Moderate tidal flooding and beach erosion will be the biggest issue.