Irene Weakens to Cat. 2, Tracks Wobble East…11am update

Hurricane Irene at 9am Friday, 26 Aug 2011


The 11am update from the National Hurricane Center indicates hurricane Irene has continued the morning trend of weakening slightly…maximum sustained winds near the eye of the storm are now 105 mph; category 2 storms have winds of 96-110 mph. Here’s the updated data from NHC as of 11am Friday:

BULLETIN
HURRICANE IRENE ADVISORY NUMBER  25
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092011
1100 AM EDT FRI AUG 26 2011

...OUTER RAIN BANDS OF LARGE HURRICANE IRENE NEARING THE COAST OF
THE CAROLINAS....

SUMMARY OF 1100 AM EDT...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...30.7N 77.3W
ABOUT 330 MI...530 KM SSW OF CAPE HATTERAS NORTH CAROLINA
MAXIMUM SUSTAINED WINDS...105 MPH...165 KM/H
PRESENT MOVEMENT...N OR 360 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...946 MB...27.93 INCHES

DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 AM EDT...1500 UTC...THE CENTER OF HURRICANE IRENE WAS
LOCATED NEAR LATITUDE 30.7 NORTH...LONGITUDE 77.3 WEST. IRENE IS
MOVING TOWARD THE NORTH NEAR 14 MPH...22 KM/H...AND THIS MOTION
IS EXPECTED TO CONTINUE TODAY. A GRADUAL TURN TOWARD THE
NORTH-NORTHEAST SHOULD BEGIN BY SATURDAY. ON THE FORECAST TRACK...
THE CORE OF THE HURRICANE WILL PASS WELL OFF THE COAST OF GEORGIA
TODAY...APPROACH THE COAST OF NORTH CAROLINA TONIGHT...AND PASS
NEAR OR OVER THE NORTH CAROLINA COAST SATURDAY.  THE HURRICANE
IS FORECAST TO MOVE NEAR OR OVER THE MID-ATLANTIC COAST SATURDAY
NIGHT.

MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 105 MPH...165
KM/H...WITH HIGHER GUSTS.  IRENE IS A CATEGORY TWO HURRICANE ON THE
SAFFIR-SIMPSON HURRICANE WIND SCALE.  LITTLE CHANGE IN STRENGTH IS
FORECAST BEFORE IRENE REACHES THE COAST OF NORTH CAROLINA.

IRENE IS A LARGE TROPICAL CYCLONE.  HURRICANE FORCE WINDS EXTEND
OUTWARD UP TO 90 MILES...150 KM...FROM THE CENTER...AND TROPICAL
STORM FORCE WINDS EXTEND OUTWARD UP TO 290 MILES...465 KM.  NOAA
BUOY 41013 LOCATED ABOUT 40 MILES SOUTH-SOUTHEAST OF SOUTHPORT
NORTH CAROLINA RECENTLY MEASURED A WIND GUST TO 47 MPH...76 KM/H.

THE LATEST MINIMUM CENTRAL PRESSURE ESTIMATED FROM RECONNAISSANCE
AIRCRAFT DATA IS 946 MB...27.93 INCHES.

Computer models tracking the storm are still in agreement in taking the center toward the outer banks of North Carolina Saturday afternoon, then north/northeast toward Ocean City, MD Saturday night into early Sunday.  There is still enough time for Irene’s track to wobble east or west, which would make a huge difference in the weather we experience here in Maryland.

European Global Model Forecast: 8am Sunday 28 Aug 2011

U.S. GFS Global Model Forecast: 8am Sunday 28 Aug 2011

This morning’s runs of the U.S. global model, the European global model, and our local in-house meso-scale RPM model show the variations that are still possible with Irene’s track.  The European model (posted first above) has the center of Irene nearly on the Delaware coast, just north of Ocean City at 8am Sunday.  The U.S. GFS global model has Irene well off the coast, southeast of New Jersey, at 8am Sunday.

RPM Model Forecast: 3pm Sunday 28 Aug 2011

RPM Upper Air Forecast: 7am Sunday 28 Aug 2011

And, our local RPM model, which has a much higher resolution, shows the center of Irene moving much slower and farther east, not reaching the latitude of Ocean City until early afternoon on Sunday, and then it is positioned a few hundred miles east of the coast.  The takeaway is that it is still too early to be certain about what exactly will happen with Irene when it moves north of Cape Hatteras.  One factor that may determine Irene’s movement, is the weak upper level trough that shows up on the RPM model’s forecast for 7am Sunday.  The trough stretches from James Bay in Canada, south across Michigan and into northern Indiana.  This little feature may be just enough to nudge Irene away from our coast, which would lessen the impact of Irene on Maryland.

RPM 72 hour Rainfall Forecast

However, for now, because the model consensus is pointing to a track closer to the coast than the RPM is showing, we should be prepared for tropical storm conditions reaching west of the bay Saturday night into midday Sunday.  That means the potential exists for the western shore to experience wind gusts of 30-50 mph, 2-6″ of rain, storm surge of 1-3 ft…on the eastern shore: wind gusts of 40-70 mph, 4-8″ of rain, storm surge of 1-3 ft…and near Ocean City: wind gusts over 70 mph, 6-10″ of rain, storm surge of 6-8 ft.

Stay tuned!

Tom Tasselmyer

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