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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: 09/16/2003 09:45 AM
 

Good Morning Philadelphia!   

We have very nice weather today.  All the better for giving you time and comfort while you put away your lawn furniture, trash cans and things that can blow around.  A large High is sitting to our southwest giving us a brief period of north winds. 

The satellite picture (around Philadelphia) is absolutely clear.  The front that just passed is out to sea to the east. 

And the radar is nice and quiet. 

But it hasn't always been so.  Over the last few days, the combination of Henri's remains, a tropical feed of moisture and the passing front brought us a LOT of rainfall in places. Chester Co. is under water in many places (just to our west).  You can see in the reds on the map that many places got more than 6" of rain.  This is very bad priming before Isabel. 

Because of that, there are already Flood Warnings for the four counties to our west.  Below is the special weather statement from the NWS telling you how to prepare for the coming storm. 

SPECIAL WEATHER STATEMENT

DEZ001>004-MDZ008-012-015-019-020-NJZ001-007>010-012>027-PAZ054-055-
060>062-067>071-161500-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
500 AM EDT TUE SEP 16 2003

...DANGEROUS HURRICANE ISABEL IS EXPECTED TO THREATEN THE MIDDLE
ATLANIC REGION THURSDAY AND FRIDAY...

HURRICANE ISABEL CONTINUES TO MOVE CLOSER TO THE EASTERN UNITED
STATES...BUT IS STILL AROUND TWO AND A HALF DAYS FROM MAKING
LANDFALL. NOW IS A GOOD TIME TO REVIEW YOUR DISASTER PLAN...AND BE
READY TO IMPLEMENT THE PLAN IF NECESSARY.

PART OF YOUR FAMILY DISASTER PLAN SHOULD BE PREPARING IN CASE A
HURRICANE THREATENS YOUR AREA.   SOME ACTIVITIES WHICH YOU STILL
HAVE TIME TO COMPLETE INCLUDE KNOWING THE HURRICANE RISKS IN YOUR
AREA SUCH AS WHETHER YOU LIVE IN A POTENTIAL FLOOD ZONE...LEARNING
SAFE ROUTES INLAND FROM COASTAL AREAS...FINDING OUT WHERE OFFICIAL
SHELTERS ARE LOCATED...TRIMMING TREES AND SHRUBBERY...CLEARING LOOSE
AND CLOGGED RAIN SPOUTS AND GUTTERS...AND DETERMINING WHERE TO MOVE
YOUR BOAT IN AN EMERGENCY.

ONE OF THE MOST IMPORTANT PARTS OF YOUR FAMILY DISASTER PLAN IS THE
PREPARATION OF A DISASTER SUPPLIES KIT.  THIS KIT SHOULD INCLUDE THE
FOLLOWING MATERIALS...A THREE DAY SUPPLY OF WATER WITH ONE GALLON
PER PERSON PER DAY...FOOD THAT WILL NOT SPOIL...ONE CHANGE OF
CLOTHING AND SHOES PER PERSON...PRESCRIPTION MEDICINES...ONE BLANKET
OR SLEEPING BAG PER PERSON...A FIRST AID KIT...A BATTERY POWERED
NOAA WEATHER RADIO AND A PORTABLE RADIO...EMERGENCY TOOLS...A
FLASHLIGHT WITH EXTRA BATTERIES...AN EXTRA SET OF CAR KEYS...AND ANY
SPECIAL ITEMS FOR INFANT...ELDERLY OR DISABLED FAMILY MEMBERS.

IF YOU HAVE A SECOND RESIDENCE NEAR THE COAST...WE RECOMMEND YOU
TAKE THE OPPORTUNITY EARLY THIS WEEK TO INSURE THAT LOOSE OBJECTS
ARE PACKED AWAY...AND YOUR RESIDENCE IS SECURE.

STAY TUNED OVER THE NEXT SEVERAL DAYS ON THE EXPECTED PATH OF
HURRICANE ISABEL.  BE PREPARED TO TAKE ADDITIONAL ACTION IF A
HURRICANE WATCH IS ISSUED FOR THE AREA. A WATCH IS ISSUED WHEN THERE
IS A POTENTIAL FOR HURRICANE CONDITIONS IN YOUR AREA WITHIN 36
HOURS. REMEMBER THAT STRONG DAMAGING WINDS AND TORRENTIAL RAINFALL
CAN EXTEND WELL INLAND WITH A MAJOR HURRICANE.

$$

MORE PREPAREDNESS INFORMATION CAN BE FOUND ON OUR WEB SITE AT
WWW.ERH.NOAA.GOV/PHI   CHECK OUT THE MENU SELECTION ENTITLED
PREPAREDNESS ON THE LEFT HAND SIDE.

AND PLEASE SEE THE FOLLOWING INTERNET SOURCES FOR ADDITIONAL
HURRICANE POTENTIAL INFORMATION AND PREPAREDNESS ISSUES...

NATIONAL HURRICANE CENTER HOME PAGE:
HTTP://WWW.NHC.NOAA.GOV

PENNSYLVANIA EMERGENCY MANAGEMENT AGENCY:
HTTP://PEMA.STATE.PA.US

MARYLAND EMERGENCY MANAGEMENT AGENCY:
HTTP://WWW.MEMA.STATE.MD.US

NEW JERSEY OFFICE OF EMERGENCY MANAGEMENT:
HTTP://WWW.STATE.NJ.US/NJOEM

DELAWARE EMERGENCY MANAGEMENT AGENCY:
HTTP://WWW.STATE.DE.US/DEMA

FEDERAL EMERGENCY MANAGEMENT AGENCY HOME PAGE:
HTTP://WWW.FEMA.GOV/HAZARDS/HURRICANES

AMERICAN RED CROSS HOME PAGE:
HTTP://WWW.RED CROSS.ORG

Also, directly from the NWS's mouth: 

From the National Weather Service Forecast Office, Mt. Holly, NJ:

...the rain we got in the past 24 hours will setup the area for potentially more flooding as any heavy rains could cause streams to rise once again. Although the track is to the west which should bring the heaviest rains to our west...we need to be concerned about some spiral bands moving onshore on the eastern side of the hurricane. This combined with upslope flow could also develop very heavy rains. I will issue an alet for potential flooding. The timing of the precipitation brings it first into Delaware late Wednesday night and then spreads the precipitation north through the area Thursday. The strongest winds will probably be Thursday night and early Friday. Users of experimental forecast grids...be aware that policy limits maximum sustained wind strength to 33 kts out past the 72 hour forecast. This is to reflect the inherent uncertainty in the hurricane forecast track at greater time ranges not the expected winds. Refer to National Hurricane Center for the official track and strength of the storm. ... Now is the time where being prepared pays off. Keep up to date with the latest forecasts. Check our web site... www.Erh.NOAA.Gov/phi   for the latest forecast information...as well as preparedness information if the hurricane threatens your location.

Looking at the Climate Stats:

We are a half inch above normal for the month, and 3 inches above normal for the year. We're fine... really. No more rain. Thanks. 

Another Dangerous aspect to prepare for are winds.
Much of the wind energy will be spent on the coastal land to the south, but the hour by hour forecast at www.accuweather.com site has winds sustained at about 30mph by 7pm Thursday with gusts to 50mph.  By 3am we may have winds 60mph (strong tropical storm winds) with gusts to 80!!!  Then ... if you believe it (I need to see it happen first) Friday 1pm to 5pm we get winds around 65mph sustained with gusts to 100 ish (hurricane force winds IN Philadelphia). 

Don't plan for this to happen, but be ready to prepare for it (if that makes sense). 

Here is a global picture of the very easy to see hurricane Isabel. 

This composite picture shows the fading out of the front to it's west as air around the storms sinks and smashes it out of the way. 

Here is yet another view of Isabel this morning...

And finally a close-up of the storm showing the eye is not clear, or as clearly defined as it has been for the last week or so. 

The rough path has it further west than earlier forecasts (College Station and Pittsburgh need to watch out as well!). 

But having it to our west is NOT the best forecast for us.  As this graphic from www.accuweather.com shows, the right front (as the storm sees it moving along) is the worst quadrant to be in. The rotation winds (counterclockwise around a Low center) add to the forward motion (which is expected to increase as it gets picked up into the trough to our west in the upper atmosphere). 

Here are the coastal areas under the gun.  Deleware is under a lower risk right now than the Carolina's, Virginian coast and the Chesapeake Bay area. 

The five day forecast has the center slide up into Canada through west central PA, with the strongest part of the storm hitting us and westward toward the center. Yikes. 

Here is the new NWS digital forecast product showing the chance of rain over the region through the end of the week.

We see in the 12 hour period ending 8am Thursday, the rain spreading in over N. Carolina and just into Virginia. 

In the next 12 hours, ending 8pm Thursday, the rain hits Philadelphia. 

From 8pm Thursday to 8am Friday, we are in the thick of it.  Wind, torrential rains, flooding, trees down. Everything. 

From Friday 8am to Friday 8pm, the rain center pulls to the north, but we could still see some strong bands of rain and/or thunderstorms pound the area. 

From 8pm Friday to 8am Saturday, the chance of rain drops off rapidly and we can start to clean up. 

Here is the landfall of Isabel from the GFS model.  This is for Thursday 8pm.  Even though the center is just onshore, the rains are already spreading FAR inland (including Philadelphia). 

And the storming continues until about Friday 8pm when it 'starts' to pull out to the north. There will be a lot of water around, and it will take a long time for some rivers and streams to go back to normal. 

Listen to your local radio and TV reports and take precautions.  Philadelphia will be in for a rough ride Thursday noon to Friday afternoon. 

Meteorologist  John Ensworth

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