NY NJ PA Weather Forecasts

Evening thoughts on Ida and potential rainfall

8:20 PM

I have some concerns about the idea that this storm isn’t coming north or at the very least is not going to have an impact on the northern Mid Atlantic.  As the dance of the models continues and the 18Z GFS shifted towards a wetter solution for the New Jersey coast again, I decided to do a comparison between the 12Z guidance of the NAM and GFS 12 hours in versus the actual 00Z observation that this guidance was suppose to forecast for.  Here are the results.

NAM:

00Z Observed Radar

NAM- 00Z Precip Forecast

So here we have the observed rainfall with actual reports of moderate to heavy rainfall extending well into central Alabama this evening and the center of Ida approaching landfall this hour.  The NAM guidance however is much slower and much further to the south.  There is barely any hint of precipitation north of the immediate coast line of Gulf Coast.  Clearly, the NAM is too far south in the expansion of precipitation further north.

GFS:

00Z Observed Radar

GFS 00Z Precip Forecast

The GFS is a bit better here with bringing the moisture further north.  However, the GFS clearly has a better handle on the situation this evening than the NAM guidance 12 hours into the forecast.  However, the GFS also has some issues in making the trough extending south from the eastern Great Lakes to the Tennessee Valley too weak.

There are some interesting observation in the water vapor satellite images this evening.  For one, the amount of moisture streaming north is very impressive.  Once again, only the GFS comes close in forecasting the expansion of upper level moisture at 300 MB being this expansive.  However, all model fall short in this department from 500 to 850 MB.  There is significant moisture streaming northward as we can see with the dark blues present in the presentation.  Also, note the Ida is now taking on strong extratropical characteristics as dry air is wrapping in behind the mid level circulation.  The mid level disturbance has now captured Ida and basically killing the warm-core low.  By tomorrow morning, I hazard a guess that Ida will be no more but a remnant low striped of the tropical moisture and latent heat energy that made the tropical low a hurricane.

Finally, we have the two upper level disturbances.  The Sub Tropical disturbance is about to interact with Ida this evening and will entrain this system completely by tomorrow morning.  Meanwhile, as the trough with the Polar jet stream progresses east, a surface cold front is slowly approaching the Mid Atlantic coast.  This cold front will become the focal point for a new low pressure development of the North Carolina coast by tomorrow evening.  The Polar jet stream disturbance currently over the northern Plains is expected to kick this whole Sub Tropical mess into the Atlantic, NOT phase.  This is key here.  The 18Z GFS brought the rain with this storm further north because of a slight phase.  Now, I don’t like to use the 18Z GFS as a forecast per say, but a good tool to see where guidance is trending.  If the 00Z guidance starts to trend towards a phase again, many forecasters will be running from sunny and dry to a very wet Wednesday and possibly Thursday time period.

For now, given the latest observational data, I like where I stand with moisture racing north along the cold front and producing a period of rainfall along the New Jersey coast on Wednesday morning.  However, I’m keeping an eye on that Polar disturbance and the development of the extratropical low pressure system off the Carolinas.  Any change in the forecast, and you’ll find it here first!

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