Jan 23: Coastal Storm Update

Jonathan Carr
By Jonathan Carr January 23, 2017 10:43

Jan 23: Coastal Storm Update

The coastal storm is well underway but peak intensity is still to come. Let’s break it down…

Right now, the primary surface low is about 988mb and tracking from W NC to OBX. Upper-level lows are closed off from 300-700mb which should keep the surface low strong as it ejects into the Atlantic Ocean and retrogrades close to the Jersey coast later today/this evening. The low’s intensity is modeled to be about 985-988mb when off the SENJ coast. This is when winds will really crank off the ocean during heavy rainfall. So right now, we’re at about 50% storm intensity with a peak intensity expected between 1PM and 10PM. The above cover image shows 850mb winds during peak conditions around 10-11PM tonight. Surface winds are less but this illustrates how strong the 850mb lower-level jet is going to be. Units are in knots. Here’s the¬†surface wind profile for 9-10pm:

namconus_mslp_wind_neus_16

There are a few trends in model guidance worth discussing. First are the increased snowfall amounts for NWNJ. The surface models that are outputting more snow are deriving their temperatures from the 850mb level which is colder. However, the strong dynamics are forcing a warm layer inward off the ocean at 700mb…where you need cold for frontogenic forcing to produce significant accumulations. This, in theory, should deform the snow production into sleet or mixed wet snowflakes. Therefore, we still feel that a pasty layer of wet snow/sleet is a more rational outcome than significant snow accumulations. I’ll continue to watch this but those are my thoughts on more snow than rain for now.

Another trend is the extension of timing. While the peak storm conditions should occur between 1PM and midnight, we will likely need all of overnight tonight and some of tomorrow for everything to clear out and wrap up. If the low lingers off the coast through most of tomorrow, then so will the rain and wind…just not as intense as it will be later today. And winds will be more northerly which will help tidal waters subside.

In English: Rain has spread into at least SNJ and parts of CNJ. Rain will continue to spread into NNJ through afternoon hours. Winds are already whipping but will really start to crank this afternoon through evening hours. During this time, I’ll be watching for “how wintry NWNJ becomes” and “how bad the coastal flooding gets” from peak onshore winds. One high tide (this morning) is down. Two more high tides to go within the period of concern…one tonight and the other early tomorrow. It wouldn’t take much for coastal flooding to be hoisted from minor-moderate to the higher end of moderate. The bottom line is that we’re in for a long 12 hours or so, especially the coast. Please be safe! JC

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Jonathan Carr
By Jonathan Carr January 23, 2017 10:43

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