At 10:35 AM, the heaviest rain is making it through Philadelphia.
The highest wind gusts will follow shortly, about 11AM to 12 noon.
A second peak in wind gusts about 2 PM—
Can we get a storm named with a more difficult pronunciation??
Tue 08:41 AM Update — graphics added below
The 2 AM (06UTC) runs of the models show the following changes in the forecast for tropical storm Isaias—
Some differences exist with areas of max rainfall.
Below is the latest GFS model accumulated rain forecast (from 2 AM, which does not include the rain from last night prior to 2AM. )
Here’s the very latest HRRR (High Resolution Rapid Refresh) hourly model from 7 AM —
Tropical Storm/Hurricane Isaias continues to move up the coastline. Very heavy rain continues to be the main threat from this storm. The heaviest rain may fall over a period of just a few hours.
The trend has been for the heaviest rain to fall slightly further west than yesterday’s model runs. Some models are predicting amounts as high as 5-7 inches of rain in some spots! The heaviest rain will fall between 11AM and 3 PM Tuesday.
The peak winds will occur around 1-2 PM. Gusts around 35-50 MPH are forecast by the latest GFS in the PHL area.
Here are the latest models with their rainfall totals –
The latest National Blend of Models (NBM version 4.0 ), often correct for QPF values, has even greater amounts—
The latest NAM NEST model has the heaviest rain more westward—
The Canadian Global (GDPS) is also a bit westward with higher amounts—
The German ICON model has a similar precip forecast—
So a generalized very heavy rain event is expected
As we can see, the forecast for today had shifted somewhat and the earlier showers and thunderstorms moved to our west before daybreak and early this morning. This wasn’t picked up until last night’s models.
For today, Sunday, most of the day will be dry and hot. High 92.6º sd 1.6º. Dew points in the 70s!
There is a chance of showers/thunderstorms this evening, between 8 PM and midnight.
With a tropical system in the picture, I expect further shifts in the forecast. The model forecasts just seem to be more ‘fluid’ when there’s a tropical storm around.
That said, the track of Hurricane Isaias appears to be taking a more inland path. Here’s the Navy COAMPS model track—
With the more inland track, the GFS (pre-release version 16) is showing 3-5+ inches of rain for our immediate Philadelphia area on Tuesday—
It will be a tropical storm or tropical storm remnant when it reaches us. The main issue will be flooding rains. Stay tuned,