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The Story Behind the Weather - By Forecaster John Ensworth M.S. - 

The Discussion of Weather Events Daily for Philadelphia and Pennsylvania

 Last updated: 09/19/2003 09:47 AM
 

Good Morning Philadelphia!   

It's blustery this morning with winds out of the South-southeast at 25mph with gusts up to about 30mph.  The rain has largely pulled out, but the clouds are still in place.  Let's pick up the pieces of the last 24 hours with the landfall of Hurricane Isabel. 

The surface map this morning shows the still a Tropical Storm Isabel in southwestern Pennsylvania.  The heaviest rain has swung around to the north and west side of the circulation center.  It looks like we are in the clear...

Rain has indeed moved on and we are in the clear around Philadelphia. 

Here is the national perspective on rainfall yesterday up to this morning.  Some areas to the south (in Virginia) received around 3-6" of rain. 

Looking closer, there was up to 5-6" in places from Lynchburg to Roanoke Rapids...

And up to 8-10" just off shore south of Morehead City (water falling back to the water...no flooding there!). 

Here at home, we received much less water from Isabel.  Philadelphia had about an inch fall in spots to the west of the city, but much lesser amounts most places.  You can see the streaks of rain dropped by thunderstorms as they rotated counterclockwise around the low center to our southwest.

Currently, Isabel still has tropical storm force winds (40mph).  It has sped up its land speed to 22mph (it was only about 4-9mph over the ocean). 

You can see its center entering Ohio at this moment with a cold front fading out in the Plains to the distant west. 

BUT the strongest winds are STILL on the right side of the storm... where WE are! The light greens and yellows are the strongest winds associated with the storm... and the central axis of these strong winds are on our heads right now. 

Here is the wedge of tropical storm force winds.  Philadelphia is dead under the center of the worst of the remaining winds.  

This is dragging warm tropical air up along the coast. 

The visible satellite picture shows clearing approaching rapidly as the storm accelerates into Canada. We should have windy sunshine in the next couple of hours. 

The infrared satellite view (showing temperatures of cloud tops or the ground in the absence of clouds) shows that there is moderately warm air all around the system (typical of a tropical storm).  One unrelated, but interesting, feature is marked with the blue line.  Here is a division between cooler north current ocean water, and the gulf stream (much warmer) water.  It is easily seen in the bone dry air caused by sinking air around the remains of Isabel. 

So looking out just a day or so... Isabel will be up in Canada north of the Great Lakes by 2am tomorrow morning, and a front will be shuffling towards us from the west. 

By Saturday night, the front will be stalling out over Pennsylvania, but will not have much punch.  A few small showers may pop up, but nothing to stand on the beach and cover for the nightly news for. 

The reason the front will die out is that you get storminess to the right of troughs, but Isabel will merge with this "Normal Mid-Latitude Trough" in the air flow in the upper atmosphere (the 500mb map is roughly at 18,000 feet).   We will be 'out of position' for the right lift to kick off storms once the front gets here (even with all this moisture in place!).

So we got an inch less rainfall than I predicted, but the winds were pretty much right on.  It could have been worse.  

Keep that hair from blowing around today and I'll see you tomorrow!

Meteorologist  John Ensworth

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