Category Archives: Tropical Storm Outlooks


Fri 08:48 AM Forecast Review — The heavy rain had a sharp westward cutoff, as eventually predicted by the models late afternoon and evening yesterday.  Here’s radar image from 4 AM  showing the the heavy rain had a strong east-west cut off—
Radar 4 AM

Updated on Thu 10:46 PM Tonight’s models have reduced the amount of rainfall and moved the heavy rain further eastward.

Updated on Thu 7:30 PM highlighted below

The latest Canadian Regional GEM model captures the sharp western cutoff in expected heavy rainfall that several afternoon models are showing—

Canadian Regional GEM rain forecast captures the sharp cutoff in heavy rain just west of the city. (Click on image for a larger view.)

The latest ICON model, which did very well with last year’s tropical storms, has the heavier rain further westward.

ICON model total rainfall. (Click on image for a larger view.)

Updated on Thu 5:59 PM highlighted below

The afternoon model runs just are becoming available. The HRRR, the GFS and the HREF have a sharper cut-off of the heavy rain just west of Philadelphia with the heaviest rain most similar to the Model Blend NBM graphic below in the original post..

Updated on Thu 1:54 PM highlighted below

With the more westward track of the storm, the latest GFS has moved in the direction of the ICON and HREF models with 1.5-3.5″ of rain, extending into the Philadelphia area.

GFS model from 12z showing accumulated rain forecast by Friday morning.

The latest ICON model (which did very good with last year’s tropical systems) has less rain accumulation-

ICON model accumulated precip forecast from 12Z today. (Click on image for a larger view.)

Model Blend (which underestimated rainfall with last year’s tropical systems)

NBM (Model Blend) total rain forecast (Click on image for a larger view.)

see my Elsa post from Monday

A cold front is approaching from the Great Lakes and a pre-frontal trough will move through Thursday afternoon. Showers and thundershowers expected after 4 PM. Most of the thunderstorm activity will be expected in the far northwest areas, with heavy rain showers later this afternoon and evening in the Philadelphia area.

The remnants of tropical storm Elsa moves in later this evening and will affect us during the night time hours. The main effects of this storm will be high precipitable water and heavy rain. Not much wind expected (30 mph gusts), mostly at the shore. The storm exits early Friday morning.

Rainfall when it ends will be in the 1.5-2.5 1.5-3.5 inch range. Exact placement of the heaviest rain a challenge. The GFS keeps much of the heavy rain in NJ while the higher resolution models and the ICON have it overspreading the Philadelphia area. The Canadian GEM has the heaviest rain near Philadelphia! I’m leaning towards the heavy rain making it into Philadelphia.

GFS 1 hour 3 hour precip forecast for 3 AM Friday morning. (Click on image for a larger view.)
HREF precip Forecast for 4AM Friday showing heavier rain into the Philadelphia suburbs. (Click on image for a larger view.)


Updated Tue 8:30 AM : The trend continues towards a westward track off the NJ coast, and a merging with a Great Lakes low and associated cold front . The remnants of Elsa are not forecast to be very strong. Just a moisture source for additional rain. Some models have the associated rain east of the storm with little effect here.

What could be more conditional than an if-else (Elsa) storm situation!

I’ve been following the path of Elsa, as forecast by the GFS, GEFS, Canadian GDPS, the ICON Global and the NBM.

The models have been showing a significantly more westward track for Elsa over the past 24 hours, bringing it closer to the NJ coastline and the Philadelphia area in the late Thursday through Friday time frame.

After several hot days Tuesday and Wednesday, an approaching cold front will bring thunderstorms as early as Wednesday evening and Thursday.

The speed of the cold front will affect the path of Elsa in our region. If the cold front slows down, we will have much more rain and wind.

The latest GFS model has several inches of rain possible this week for the Philadelphia area and eastward, but the NBM rainfall amounts are not impressive right now.

Here’s the current GFS model forecast for 7 PM Thursday—

GFS model forecast (simulated radar, cloud cover) for 7 PM Thursday. This represents a significant change over the past day to a more westward track . (Click on image for a larger view.)

These tropical storm forecasts always to change over time. Stay tuned.