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lrene's Heavy Rain Impacts in PHL 8/29 - 8/31


ptb127

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These models are still clueless. We went from >4.00" to <0.25" rain from 18z to 0z on the NAM...

Regardless of where it ends up, the western edge will be very sharp..I don't envy the NWS/NHC forecasters on this one.

I-81 always gets the shaft. It's been this way for quite awhile now with regard to major storm events.

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There will be weeping and gnashing of teeth in about 48 hours from some because they didn't get the worst case. ;)

I suspect you are quite correct... noticed she isn't looking all that great this morning and NHC dropped it to strong cat 2. Seems weird given the 942 central pressure, but given the large size, the gradient probably isn't as strong as you might normally expect in a normal-sized hurricane. I suspect this will also make a difference up the coast, where despite a very low pressure, winds may not be as strong as some fear. Gloria was 961 mb at landfall on LI, btw... something to think about.

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Here's Gloria's rainfall and track... note it was cat 1/cat 2 when it passed NJ and made landfall with 961 mb pressure on LI... most of NJ didn't gust to hurricane force (TTN peak gust was 52 mph). Still enough to bring some trees and power lines down...

post-39-0-89877100-1314352218.gif

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Here's Gloria's rainfall and track... note it was cat 1/cat 2 when it passed NJ and made landfall with 961 mb pressure on LI... most of NJ didn't gust to hurricane force (TTN peak gust was 52 mph). Still enough to bring some trees and power lines down...

True. I will say even with winds that didn't max out over 90 mph on Long island in Gloria, it did knock out power for 1-2 weeks in some areas (8 days for me). Tree damage was substancial too.

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I suspect you are quite correct... noticed she isn't looking all that great this morning and NHC dropped it to strong cat 2. Seems weird given the 942 central pressure, but given the large size, the gradient probably isn't as strong as you might normally expect in a normal-sized hurricane. I suspect this will also make a difference up the coast, where despite a very low pressure, winds may not be as strong as some fear. Gloria was 961 mb at landfall on LI, btw... something to think about.

I asked about that in the main forum -- Earl had a low pressure (950's IIRC) but couldn't produce a wind gust higher than a fart outside of the Outer Banks and Cape Cod because the ambient pressure on the East Coast was rather low and there was no real gradient on the north/west side between Earl and a high (in fact I don't think there was a real surface high nearby). I kinda worry that's an issue here. Might be a nasty storm but wouldn't surprise me if Irene final landfalls on LI with 65-70 mph max winds and 950's pressure.

I've hedged my wind predictions to 80 mph gusts at the Shore, 50-60 mph gusts on I-95, lower inland -- and I'm probably too high I think.

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I asked about that in the main forum -- Earl had a low pressure (950's IIRC) but couldn't produce a wind gust higher than a fart outside of the Outer Banks and Cape Cod because the ambient pressure on the East Coast was rather low and there was no real gradient on the north/west side between Earl and a high (in fact I don't think there was a real surface high nearby). I kinda worry that's an issue here. Might be a nasty storm but wouldn't surprise me if Irene final landfalls on LI with 65-70 mph max winds and 950's pressure.

I've hedged my wind predictions to 80 mph gusts at the Shore, 50-60 mph gusts on I-95, lower inland -- and I'm probably too high I think.

I don't think your prediction is unreasonable.

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:lol: well have fun ;)

Yeah. If I go, I'll enjoy it. Problem is, I don't want to leave my house here in Pennsylvania "if"" things are nasty here.

. I'm hoping its just alot of rain here in the NW Philly burbs and 20-30 mph winds....if it looks more extreme here, then I won't feel comfortable leaving.

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Morning AFD from Mount Holly, nice writeup Mike.

.LONG TERM /SATURDAY THROUGH THURSDAY/...

-- Changed Discussion --**DAMAGING AFFECTS FROM HURRICANE IRENE SATURDAY AND SUNDAY ACROSS

THE REGION.** EVERYONE SHOULD BE PREPARING FOR THIS LARGE STORM AS

NOW IS THE TIME. HAVE A PLAN IN PLACE, LISTEN TO LOCAL OFFICIALS

REGARDING ANY EVACUATIONS AND KEEP UPDATED ON THE WEATHER

FORECASTS. SOME EVACUATIONS HAVE ALREADY STARTED ALONG THE NEW

JERSEY COAST. THE 5 AM NHC ADVISORY HAS BEEN INCORPORATED INTO OUR

WIND GRIDS. IN ADDITION, THE EARLIER WATCHES WERE UPGRADED TO

WARNINGS WITH SOME NEW WATCHES ADDED ACROSS THE NORTHERN PART OF

THE CWA. PLEASE NOTE THAT HUNTERDON COUNTY, NEW JERSEY IS UNDER

A TROPICAL STORM WATCH, HOWEVER DUE A SOFTWARE GLITCH IT IS NOT

SHOWING UP IN THE HLS PRODUCT. WE HOPE TO GET THIS CORRECT AS

SOON AS POSSIBLE.

THE MAIN FOCUS FOR THIS PERIOD IS THE TRACK AND IMPACTS OF

HURRICANE IRENE. WE WANT TO STRESS THAT IT IS IMPORTANT TO NOT

FOCUS ON THE EXACT CENTER OF THE STORM, AS IT IS FORECAST TO BE A

LARGE SYSTEM AS IT MOVES THROUGH. WE EXPECT EXTENSIVE IMPACTS FROM

THIS HURRICANE ACROSS THE ENTIRE CWA REGARDLESS OF THE TRACK JUST

INLAND, ON THE COAST OR ABOUT 50 MILES OFFSHORE. THE PEAK OF THE

STORM LOOKS TO GENERALLY OCCUR SATURDAY NIGHT THROUGH ABOUT MIDDAY

SUNDAY. WE WANT TO STRESS THAT THERE IS A RATHER HIGH RISK OF

DAMAGING WINDS AND HEAVY AND POSSIBLY RECORD SETTING RAINFALL

LATER SATURDAY AND SUNDAY.

DESPITE THE FORECAST TRACK OF THE HURRICANE AMONG THE MODELS

WAFFLING BACK AND FORTH SOME DURING THE LAST FEW DAYS, WE WILL

HAVE IMPACTS FROM THIS SYSTEM. THE FINER DETAILS WILL ULTIMATELY

DEPEND ON WHERE THE CENTER TRACKS, WHICH INCLUDES THE SWATH OF

STRONGEST WINDS AND STORM SURGE. THE FIRST UPPER-LEVEL TROUGH IS

FORECAST TO SHIFT NORTHEAST OF THE AREA TODAY LEAVING A WEAKNESS

BETWEEN THE RIDGE IN THE WESTERN ATLANTIC AND ANOTHER UPPER-LEVEL

TROUGH WELL TO THE WEST. THIS WILL SERVE AS A CONDUIT FOR A

NORTHWARD MOTION FOR THE HURRICANE, ALTHOUGH SOME TURN TO THE

NORTH-NORTHEAST IS EXPECTED WITH TIME. ANY LAND INTERACTION PRIOR

TO THE HURRICANE ARRIVING INTO OUR AREA WILL SERVE TO WEAKEN IT,

HOWEVER WE ARE ANTICIPATING RAIN AND INCREASING WIND TO ARRIVE

WELL BEFORE THE CENTER. THIS WILL BE COURTEOUS OF A COASTAL TYPE

FRONT IN PLACE AND A WEALTH OF MOISTURE SURGING INLAND FROM A

STRENGTHENING ONSHORE FLOW.

THE FORWARD SPEED OF HURRICANE IRENE IN CONJUNCTION WITH THE

TIMING AND AMPLIFICATION OF THE INCOMING TROUGH IS CRUCIAL IN

DETERMINING THE WESTERN EXTENT OF THE HURRICANES TRACK. THIS IS

DANGEROUS AS A LATER TIMING IN THE TROUGH AMPLIFYING SOME MORE

WILL TEND TO ALLOW THE HURRICANE TO TRACK FARTHER WEST. OUR WIND

FORECAST IS BASED OFF OF THE GRIDDED WIND FIELD FROM THE OFFICIAL

NHC FORECAST AND THIS WILL BE UPDATED WITH SUBSEQUENT ADVISORY

ISSUANCES. WE GENERALLY BASED OUR POPS MORE TOWARD A BLEND WHICH

ENDS UP SIMILAR TO THE GFS. IF THE CENTER TRACKS FARTHER OFF THE

COAST, THEN THERE MAY BE A RATHER TIGHT GRADIENT IN THE RAIN

SHIELD ACROSS THE CWA FROM EAST TO WEST. IF THE STORM SHIFTS TO AN

INLAND TRACK, THEN THE AXIS OF HEAVIEST RAIN WILL SHIFT AND THE

THREAT OF TORNADOES WILL INCREASE. THERE CONTINUES TO BE A HIGH

RISK OF IMPACTS WITH THIS HURRICANE, WHICH INCLUDES WIDESPREAD

DAMAGING WINDS, TORRENTIAL RAIN, COASTAL FLOODING, DANGEROUS RIP

CURRENTS, AND BATTERING WAVES AND BEACH EROSION. FOR THE HEAVY

RAIN ASPECT, SEE THE HYDROLOGY SECTION BELOW.

INTERESTING TO NOTE THAT MUCH OF THE MODEL GUIDANCE DEVELOPS A

STRONG 250 MB JET NORTH OF THE HURRICANE SATURDAY INTO SUNDAY,

GENERALLY FROM THE EASTERN GREAT LAKES TO NORTHERN NEW ENGLAND.

THIS UPPER-LEVEL JET EVEN HAS SOME ANTICYCLONIC CURVATURE TO IT

AND GIVEN THE ORIENTATION OF THIS JET IT IS SUCH THAT IRENE IS

WITHIN THE RIGHT ENTRANCE REGION AS SHE TRACKS NORTHWARD. THIS

SCENARIO MAY TEND TO HELP WITH A POLEWARD UPPER-LEVEL OUTFLOW

CHANNEL AND ASSIST IN THE INTENSITY OF THE SYSTEM AS A WHOLE.

THEREFORE, DESPITE SOME INCREASING SHEAR AS THE HURRICANE GAINES

LATITUDE ALONG WITH COOLER WATERS AND LAND INTERACTIONS, PERHAPS

THIS IS WHY MUCH OF THE MODEL GUIDANCE NEARLY INSISTS THIS SYSTEM

REMAINS A POWERFUL ONE ALL THE WAY INTO SOUTHERN NEW ENGLAND. IT

BECOMES EVEN MORE OF AN INTENSITY FORECAST CHALLENGE AS TROPICAL

CYCLONES GET THIS FAR NORTH AND INTERACT WITH BAROCLINIC ZONES AND

LARGE SCALE SYNOPTIC FEATURES. AN EXAMINATION OF THE WIND FIELD AT

925 MB IS CONCERNING WITH A LARGE AREA OF 60 TO NEARLY 85 KNOTS

RACKING ACROSS THE CWA SATURDAY EVENING THROUGH SUNDAY MORNING.

WHILE THE FRICTIONAL EFFECTS WILL TEND TO SLOW THE WIND DOWN SOME

AND ALSO ALLOW FOR SOME DECOUPLING BETWEEN THE SURFACE AND ABOVE,

THE PRESSURE GRADIENT COMBINED WITH ENHANCED MIXING WITHIN HEAVIER

RAIN/CONVECTION SHOULD PRODUCE SIGNIFICANT/DAMAGING GUSTS. WE

CONTINUE TO USE A 125 PERCENT OF THE SUSTAINED WINDS TO DERIVE OUR

GUSTS BUT CAPPED THEM AT 90 KNOTS /20 PERCENT REDUCTION OF THE

SUSTAINED WINDS OVER LAND/. THE WIND GUST TOOL THAT INCLUDES

MIXING MAY BE TO HIGH ESPECIALLY OVER AREAS FARTHER INLAND. THERE

SEEMS TO BE A GROWING MODEL CONSENSUS EARLY THIS MORNING THAT THE

HURRICANE MAY END UP MOVING A BIT FASTER THAN EARLIER ADVERTISED

AS IT GETS TO OUR CWA. WE THEREFORE STARTED TO TAPER THE POPS DOWN

A BIT FASTER FROM SOUTH TO NORTH SUNDAY.

ONCE THE STORM MOVES OFF TO THE NORTH AND NORTHEAST LATER SUNDAY,

THE CONDITIONS WILL QUICKLY IMPROVE. OVERALL A MUCH CALMER TIME

FRAME MONDAY THROUGH THURSDAY AS THE WIND WILL QUICKLY DIMINISH

MONDAY AS HIGH PRESSURE BEGINS TO BUILD IN. A WEAK TROUGH WILL

SKIRT OUR REGION TUESDAY, WHICH MAY INCREASE CLOUDS A BIT. HIGH

PRESSURE THEN BUILDS ACROSS ON WEDNESDAY BEFORE SLIPPING TO THE

EAST THURSDAY.-- End Changed Discussion --

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Here's Gloria's rainfall and track... note it was cat 1/cat 2 when it passed NJ and made landfall with 961 mb pressure on LI... most of NJ didn't gust to hurricane force (TTN peak gust was 52 mph). Still enough to bring some trees and power lines down...

We had almost 8" of rain with Glora. Much well before the winds arrived. Before Gloria it was very dry. Completely different now.

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We had almost 8" of rain with Glora. Much well before the winds arrived. Before Gloria it was very dry. Completely different now.

The one saving grace west of the city may be that there's a rather sharp QPF cutoff between Coatesville/Reading and Lancaster...not sure how far west/east that cutoff gets but wouldn't surprise me if western Berks gets less than an inch while Pottstown gets 5".

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