Sandy: Some NHC wind probabilities/forecast discussions for a few cities in the storm’s path

The National Hurricane Center publishes a wind probabilities chart along with its discussion and forecast of ongoing storms. It’s worth checking out.

For example, the current NHC probabilities chart for Sandy shows the following cities might get sustained low-end tropical storm winds (34 knots or 39 mph), mid-range tropical storm winds (50 knots or 58 mph) and/or high-end tropical storm/low-end Category 1 hurricane winds (64 knots, 74 mph).

(Note: There are many other places listed on each wind probabilities chart. The most recent one is accessible on the NHC page for Sandy.)

ocean city, md

Ocean City, Maryland. (Source)

Ocean City, Maryland

This city tops all three categories, with the NHC currently giving it a 52% chance of experiencing 1-minute sustained 34-knot/39-mph winds between now and Tuesday morning, October 30th. Ocean City has a 21% chance of experiencing 1-minute sustained 50-knot/58-mph winds over the same period, and a 7% chance of 64-knot/74 mph winds.

What are the National Weather Service meteorologists for Ocean City saying in their current forecast discussion, you ask? Quite a bit.

HURRICANE SANDY WILL MOVE FM OFF THE FL COAST NNE TO WELL EAST OF
THE NC OUTER BANKS BY 00Z MON. PLEASE REFER TO WWW.NHC.NOAA.GOV
FOR THE LATEST FORECAST TRACK FOR SANDY. THERE IS A CHANCE FOR
SHOWERS LATE THIS EVENING AND OVERNIGHT OVR SRN VA/NE NC…AS
SPOKES OF MOISTURE EJECTING FM SANDY LIFT NWD AND INTERACT WITH
THE REMNANTS OF A WEAK BOUNDARY. LOWS TNGT WILL RANGE FM THE MID
50S TO LWR 60S.

SAT THRU SUN…AS SANDY TRACKS NNE TO WELL EAST OF THE NC OUTER
BANKS…[snip] AT THIS TIME…EXPECTING HEAVIEST RAINS TO AFFECT
ERN THIRD OF THE REGION THRU SUN…WITH AMTS RANGING FM 1.5 INCHES
OVR LWR MD TO AS MUCH AS 4.5 INCHES OVR CSTL NE NC. THERE REMAINS
SOME UNCERTAINTY REGARDING THE STORM TRACK FM SUN AND BEYOND…SO
THESE RAINFALL TOTALS THRU SUN COULD CHANGE.

COASTAL AREAS WILL LIKELY EXPERIENCE STRONG SUSTAINED WINDS OF
25-30 MPH WITH GUSTS OF 40-50 MPH AND HEAVY RAIN SAT NGT THRU
SUN. INLAND AREAS WILL ALSO EXPERIENCE BREEZY WINDS OF 15-20 MPH
WITH GUSTS 30 TO 40 MPH ALONG WITH MODERATE TO HEAVY RAIN AT TIMES
DURING THE SAME TIMEFRAME…ESPLY ALONG AND EAST OF I95. KEEP IN
MIND THAT IF THE STORM TRACK SHIFTS CLOSER TO THE COASTLINE…THEN
INLAND AREAS WOULD EXPERIENCE MORE INTENSE RAINFALL AND STRONGER
WINDS.

HIGHS ON SAT IN THE UPR 60S TO LWR 70S…AND IN THE UPR 50S TO MID
60S ON SUN. DEPENDING ON TIMING OF CLOUD COVER ASSOCIATED WITH
SANDY…TEMPS ON SAT MAY NEED TO BE LOWERED. LOWS SAT NGT IN THE
50S (ARND 60 IMMEDIATE COAST).

.LONG TERM /SUNDAY THROUGH THURSDAY/…
GIVEN CONTINUED TWEAKS TO THE NHC TRACK OF SANDY…AND W/ NEW
00Z/26 SUITE OF MODELS…HAVE MADE SOME CHANGES TO THE SUN NIGHT-TUE
PORTION OF THE EXTENDED PERIOD. MOST SIGNIFICANTLY…HAVE GENLY
BUMPED WIND SPEEDS UP BY ABOUT 10 KT AREA-WIDE FROM PREVIOUS FCST.
STARTING AT 00Z/MON THE LATEST ECMWF AND GFS ARE NOT ALL THAT
DIFFERENT…WITH A RATHER LARGE SHIFT THEREAFTER. THE 00Z/26 ECMWF
IS ACTUALLY A TAD FASTER BUT WEAKER THAN ITS 12Z/25 RUN (BUT STILL
STRONGER AND ABOUT 1.5 DEG LAT FARTHER WEST THAN THE GFS). THE
LATEST NHC TRACK IS GENLY A COMPROMISE OF THIS POSITION…SLIGHTLY
FAVORING THE MORE CONSISTENT ECMWF AS THE VARIOUS TROPICAL MODELS
ARE CLOSER TO THIS SOLUTION AS WELL.

AS FOR THE STRENGTH OF THE SYSTEM…PER HPC DISCUSSION…THE
DETERMINISTIC GUIDANCE (CANADIAN, ECMWF, AND GFS INCLUDED) HAS SHOWN
A TENDENCY TOWARDS OVER-DEEPENING TROPICAL CYCLONES AS THEY GAIN
LATITUDE AND/OR UNDERGO EXTRA-TROPICAL TRANSITION OVER THE PAST
COUPLE YEARS…CENTRAL PRESSURE WILL NOT BE NEARLY AS LOW AS EITHER
THE GFS OR ECMWF. STILL…THE PRESENCE OF A 965-970 MB LOW WEST OF
70 W LONGITUDE ON MON WILL LEAD TO STORM FORCE WINDS ACRS THE AKQ
COASTAL WATERS..AND POSSIBLY THE BAY AND CURRITUCK SOUND. OVER
LAND…SUNDAY NIGHT/MON WILL SEE SUSTAINED WINDS OF 30-45 MPH NEAR
THE COAST AND 20-30 MPH INLAND…WITH GUSTS TO 45-55 MPH NEAR THE
COAST AND 30-45 MPH INLAND. DEPENDING ON THE CHARACTERISTICS OF
SANDY AT THIS POINT (TROPICAL VS. EXTRA- TROPICAL)…IT IS LIKELY
THAT EITHER A WIND ADVISORY OR TROPICAL STORM WATCH WILL BE IN
EFFECT FOR PORTIONS OF THE CWA.

CONTINUED VERY WINDY MON NIGHT/TUE (WITH MORE HEADLINES POSSIBLY
NEEDED) ALTHOUGH MORE UNCERTAINTY ARISES AS MODELS DIVERGE MORE IN
THEIR POSITION AND THE SUBSEQUENT PRESSURE GRADIENT SETUP. OVERALL
THOUGH…TRANSITION WILL BE TO MORE OFFSHORE/NW OR W FLOW AS COLD
AIR WRAPS INTO THE SYSTEM FROM THE MIDWEST.

WILL CONTINUE WITH UNSETTLED/CLDY AND COOL WX WITH CHC TO LIKELY
POPS FOR RAIN SUN EVENING THRU MON NGT…THEN DIMINISHING TO CHC OR
SLGT CHC POPS FOR TUE AND TUE NGT.

Atlantic City from Caesars

Atlantic City from Caesar’s third floor. (LancerE)

Atlantic City, New Jersey

Atlantic City comes in second across the board, with 51% chance of having low-end tropical storm winds, 19% chance of mid-range tropical storm force winds and 6% chance of 64-knot/74-mph winds (it’s tied with Cape Hatteras here).

The NWS forecasters responsible for the Atlantic City forecast have this to say in their current discussion:

.LONG TERM /SATURDAY THROUGH THURSDAY/…
THE MAIN FOCUS IN THE EXTENDED REMAIN CENTERED AROUND HURRICANE
SANDY AND ITS POSSIBLE EFFECTS ON OUR REGION. ON SATURDAY, A FRONTAL
BOUNDARY IS FORECAST TO BE APPROACHING THE AREA FROM THE WEST, BUT
WILL LIKELY STALL ACROSS CENTRAL PENNSYLVANIA OVER THE WEEKEND AS
SANDY MOVES NORTHWARD. AS THE BOUNDARY REMAINS STATIONARY THROUGH
THE WEEKEND, IT WILL LIKELY DRAW SOME MOISTURE FROM SANDY AND ANY
DISTURBANCES ALOFT COULD HELP ENHANCE PRECIPITATION ACROSS THE AREA.
WE MAINTAIN CHANCE POPS, INCREASING TO LIKELY POPS FOR SATURDAY
THROUGH SUNDAY.

THE FOCUS THEN TURNS TO HURRICANE SANDY. THERE IS STILL QUITE A
SPREAD IN MODEL GUIDANCE IN REGARDS TO THE TRACK AND TIMING OF THE
STORM. THE ECMWF CONTINUES WITH THE MOST SOUTHERN TRACK OF THE
STORM TAKING IT ACROSS THE SOUTHERN DELMARVA, WHILE THE CANADIAN
TRACK THE STORM WELL NORTH INTO MAINE. THE GFS IS BETWEEN THE TWO
MAKING LANDFALL JUST EAST OF LONG ISLAND, NEW YORK. THE LATEST NHC
FORECAST TRACK KEEPS CONTINUITY AND HAS SANDY MAKING LANDFALL NEAR
SOUTHERN DELAWARE TUESDAY MORNING. WITH THIS WE HAVE BEGUN TO
INCREASE WINDS ACROSS THE AREA DURING THE MONDAY INTO TUESDAY TIME
PERIOD. WE ALSO MAINTAIN A LIKELY POPS ACROSS THE AREA FOR MONDAY
INTO TUESDAY. EVEN WITH THE SPREAD IN THE GUIDANCE, ANY OF THE
SOLUTIONS WILL GIVE OUR AREA A PRETTY SIGNIFICANT IMPACT, RANGING
FROM HEAVY RAINS, TO STRONG WINDS, AND COASTAL FLOODING. CONTINUE
TO FOLLOW THE LATEST TRACK UPDATES WITH THE NATIONAL HURRICANE
CENTER.

AFTER SANDY MAKES LANDFALL, THE REMNANTS OF THE STORM ARE EXPECTED
TO SLOWLY DRIFT INTO NEW ENGLAND/SOUTHEASTERN CANADA THROUGH THE END
OF THE WEEK. TROUGHING ALOFT WILL REMAIN ACROSS THE EAST COAST WHICH
WILL KEEP TEMPERATURES CLOSE TO, OR SLIGHTLY BELOW NORMAL. THERE
WILL ALSO REMAIN A SMALL CHANCE OF SHOWERS

Church in Dover Delaware

Presbyterian church in Dover, Delaware (Jim Bowen)

Dover, Delaware

Dover also places across the board, in third place, with a 48% chance of 34-knot/39-mph winds between now and Tuesday, a 16% chance of 50-knot/58-mph winds, and a 5% chance of 64-knot/74-mph winds.

Their forecast discussion is the same as for Atlantic City.

East River flooding during Irene

East River flooding in New York during 2011’s Hurricane Irene (Marianne O’Leary)

New York City

The Big Apple places fourth across the board, but it’s tied with other cities in two of the wind speed probabilities.

It has a 43% chance of experiencing those 34-knot/39-mph winds, actually a bit higher likelihood than Cape Hatteras as well as Newark, both of which have probabilities of 42%. New York and Cape Hatteras are tied at 14% likelihood of 50-knot/58-mph winds between now and Tuesday, while it’s a scramble between New York. Trenton, Baltimore, and Norfolk for the unenviable chance (4%) of experiencing sustained 64-knot/74-mph winds over the same time period.

Here is how forecasters for New York City are discussing it currently:

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/…
POTENTIAL FOR A DANGEROUS COASTAL STORM EARLY NEXT WEEK…

COMPLEX UPPER PATTERN ACROSS THE CONUS AND INTO THE WESTERN ATLANTIC
THIS WEEKEND INTO NEXT WEEK. A DEEP UPPER TROUGH EXTENDING FROM THE
UPPER MISSISSIPPI VALLEY AND GREAT LAKES REGION THROUGH THE LOWER
MISSISSIPPI VALLEY AND SOUTHEASTERN STATES IS FORECAST TO BECOME
NEGATIVELY TILTED ON SUNDAY. MEANWHILE…A REX BLOCK DOWNSTREAM OVER
THE NORTHERN ATLANTIC WILL INHIBIT THE EASTWARD PROGRESSION OF ANY
SYSTEMS OVER THE WESTERN ATLANTIC AND NOAM. THE COMBINATION OF THESE
TO UPPER FEATURES INCLUDING JUST HOW NEGATIVELY TILTED THE UPPER
TROUGH BECOMES WILL ULTIMATELY DETERMINE THE EXACT TRACK OF SANDY.

CONFIDENCE CONTINUES TO INCREASE THAT THE LOCAL AREA WILL BE
AFFECTED BY IMPACTS FROM SANDY. 00Z/26 MODEL SUITE CONTINUES TO SHOW
LANDFALL OF THIS SYSTEM ANYWHERE BETWEEN THE DELMARVA TO
MAINE…ALTHOUGH THE HURRICANE MODELS INDICATE A MORE CONCENTRATED
CLUSTERING BETWEEN EASTERN LONG ISLAND TO THE TIP OF THE DELMARVA
PENINSULA. HAVE CONTINUED WITH THE PREVIOUS FORECAST BEYOND SUNDAY
NIGHT…ALTHOUGH HAVE MADE SOME ADJUSTMENTS BASED ON LATEST NHC
GUIDANCE. THE LATEST NHC GUIDANCE TAKES SANDY INTO THE SOUTHERN NJ/
DELMARVA COAST LATE MON NIGHT/TUE MORNING…ALTHOUGH WHETHER THE
STORM WILL BE POST-TROPICAL BY THIS POINT REMAINS IN QUESTION.
NEVER-THE-LESS…THE STORM IS VERY LARGE AND REGARDLESS WHETHER IT
IS TROPICAL OR NOT WILL STILL BE A POWERFUL AND HISTORIC STORM IN
THE NORTHEAST/MID ATLANTIC.

A WEAKENING COLD FRONT APPROACHING FROM THE WEST MAY RESULT IN SOME
SHOWERS ACROSS WESTERN ZONES SAT NIGHT…WITH RAIN BANDS FROM SANDY
ALSO APPROACHING FROM THE S. EASTERLY WINDS WILL ALSO INCREASE AS
THE PRES GRADIENT TIGHTENS. WITH THE INCREASING EAST TO NORTHEAST
FLOW AND A NEW MOON EXPECTED ON MONDAY…COASTAL FLOODING CONCERNS
MAY DEVELOP AS EARLY AS SUNDAY. NORTHEAST WINDS INCREASE SUNDAY INTO
MONDAY AND ARE CURRENTLY EXPECTED TO BE HIGHEST FROM LATE MONDAY
NIGHT THROUGH TUE ATTM WITH THE POTENTIAL FOR SPEEDS OF
45-50G70-80MPH…SLIGHTLY HIGHER IN ELEVATED LOCATIONS. WHAT MAKES
THIS ESPECIALLY DANGEROUS IS THAT THIS COULD BE A PROLONGED
EVENT…WITH WINDS OF THIS MAGNITUDE LASTING ANYWHERE FROM 18-30
HOURS. THIS WOULD BATTER THE COASTS…LEADING TO WIDESPREAD DOWNED
TREES AND POWER LINES AND POTENTIALLY SIGNIFICANT COASTAL FLOODING
AND BEACH EROSION. STILL TOO EARLY TO DETERMINE EXACT RAINFALL
AMOUNTS…BUT FLOODING RAINS ARE A DISTINCT POSSIBILITY.

ONCE AGAIN…UNCERTAINTY REMAINS WITH THIS FORECAST WITH THE
GUIDANCE STILL SUPPORTING MANY DIFFERENT LOW TRACK SCENARIOS. REFER
TO THE NATIONAL HURRICANE CENTER FOR THE LATEST TRACK AND FORECASTS.

A Different Kind of Storm

This will evolve over time, of course, but we’re pretty close to the main event now.

I’ve noticed that these probabilities tend to verify quite well during the hurricane season, but it’s important to keep in mind what the National Hurricane Center forecaster noted yesterday: the probabilities aren’t designed to handle nontropical systems, and that is what Sandy is going to turn into soon. There is a bit more uncertainty with this storm than with others.

Mohawk River in flood at Cohoes after Hurricane Irene in 2011

Mohawk River in flood at Cohoes after Hurricane Irene in 2011.

Here is what my own weather office in Albany, NY, is saying in its current forecast discussion:

.LONG TERM /MONDAY THROUGH THURSDAY/…
NOT MANY CHANGES MADE TO PREVIOUS LONG TERM GRIDS…WITH THE
EXCEPTION OF INCREASING TUE NT POPS INTO THE LIKELY RANGE…AND
INCORPORATING NHC WIND TOOL FOR MON-EARLY TUE.

MODELS CONTINUE TO FAVOR A TRACK OF A POWERFUL HYBRID SYSTEM TOWARD
THE NORTHERN MID ATLANTIC OR NEW ENGLAND COAST EARLY NEXT WEEK. THE
00Z/26 ECMWF REMAINS VERY CONSISTENT…TRACKING THE CENTER OF THE
STORM INTO THE DELMARVA PENINSULA…WHILE THE 00Z/26 GFS TRACKS THE
CENTER TOWARD LONG ISLAND. THE 00Z/26 NAM ALSO TRACKS THE SYSTEM
TOWARD LONG ISLAND…ALBEIT MORE FROM THE SOUTH. ALL MODELS CONTINUE
TO ADVERTISE A POTENTIALLY VERY LOW CENTRAL PRESSURE…GENERALLY SUB
960 MB WITH THE EXCEPTION OF THE NAM. HOWEVER…AS HPC INDICATED IN
THE LATEST PMDHMD…MOST DETERMINISTIC MODELS AS OF LATE HAVE HAD A
BIAS IN OVER-DEEPENING TROPICAL CYCLONES AS THEY MOVE POLEWARD
AND/OR TRANSITION INTO AN EXTRATROPICAL ENTITY…SO ULTIMATELY THE
CENTRAL PRESSURE MAY NOT BE NEARLY AS LOW AS CURRENT MODELS
INDICATE. NEVERTHELESS…A POWERFUL STORM IS LIKELY TO AFFECT A
LARGE PORTION OF THE REGION…MAINLY MONDAY INTO TUESDAY…ALTHOUGH
SOME RAIN AND WIND MAY DEVELOP LATE SUNDAY INTO SUN NT…AND COULD
LINGER INTO TUE NT OR WED.

AS FAR AS POTENTIAL IMPACTS ON THE ALBANY CWA…AT THE VERY
LEAST…IT APPEARS THAT STRONG WINDS AND A PERIOD OF HEAVY RAIN
SHOULD OCCUR SOMETIME DURING THE MON-TUE TIMEFRAME. THIS COULD
ENTAIL WIDESPREAD WINDS OF 30-50 MPH…WITH POTENTIALLY STRONGER
GUSTS IN EXCESS OF 50 MPH…ESP ACROSS HIGHER ELEVATIONS SUCH AS THE
GREEN MOUNTAINS/BERKSHIRES/TACONICS…AND ACROSS PORTIONS OF THE
EASTERN CATSKILLS. DEPENDING ON THE ULTIMATE TRACK…SUCH AS ONE
SIMILAR TO THE 00Z/26 GFS…SHOULD A MORE NORTHERLY FLOW
DEVELOP…THEN CHANNELED FLOW DOWN THE HUDSON RIVER VALLEY COULD
ALSO LEAD TO WINDS IN EXCESS OF 50 MPH IN VALLEY REGIONS.

AS FOR RAINFALL…AGAIN THIS WILL ULTIMATELY DEPEND ON THE EXACT
TRACK. AT THE VERY LEAST…AREAS OF THE CATSKILLS…AND ALSO THE
GREENS/BERKSHIRES/TACONICS WOULD POTENTIALLY WITNESS STRONG
OROGRAPHICAL EFFECTS WHICH COULD GREATLY ENHANCE RAINFALL AMTS. AT
THE SAME TIME…THERE IS SOME POSSIBILITY THAT IF LOW LEVEL WINDS
REMAIN MORE FROM THE NE…SUCH AS INDICATED IN THE GFS
SOLUTION…THAT SIGNIFICANTLY LESS RAINFALL COULD OCCUR IN VALLEY
LOCATIONS DUE TO STRONG DOWNSLOPING.

LAST BUT NOT LEAST…THERE IS A POSSIBILITY OF TIDAL FLOODING FOR
AREAS ADJACENT TO THE HUDSON RIVER…AGAIN HIGHLY DEPENDENT ON THE
ULTIMATE TRACK. THIS WOULD BE A GREATER CONCERN SHOULD THE STORM
TRACK SLIGHTLY FURTHER SOUTH…SUCH AS INTO THE DELMARVA REGION OR
NEW JERSEY…AS A PERSISTENT STRONG EASTERLY COMPONENT TO OUR SOUTH
WOULD TEND TO DRIVE WATER INTO AREAS WHERE THE HUDSON RIVER NORMALLY
EMPTIES…IN ADDITION TO THE FACT THAT ASTRONOMICAL TIDES WILL BE
HIGHER DUE TO NEXT WEEK/S FULL MOON.

AGAIN…THE TRACK AND EVOLUTION OF THIS STORM IS VERY ATYPICAL…AND
WITH SOME UNCERTAINTY LINGERING IN THE EXACT TRACK/EVOLUTION…THE
AFOREMENTIONED POTENTIAL EFFECTS COULD EASILY CHANGE WITH SUBSEQUENT
UPDATES.

I’ll schedule Monday’s Civil War Anniversary post in advance, just in case we lose power Sunday or Monday, though that’s probably not too likely up here north of the forecast track and 150 miles inland. It will be a big storm, just in terms of diameter, though. We’ll see.

Stay safe, everybody!



Categories: Weather

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