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NWS Warning and Product Changes Associated with Post-Tropical Cyclones


Service Change Notice
4 April 2013

Beginning 1 June 2013, the National Weather Service (NWS) is adopting two important changes in the way it handles post-tropical cyclones (closed areas of low-pressure that were once tropical cyclones but no longer qualify for that designation). These changes were motivated by experiences associated with Hurricane Sandy last fall. The first of these changes gives the NWS the option to continue issuing formal advisories on post-tropical cyclones, in those cases when the system continues to pose a significant threat to life and property, and when a transfer of responsibility to another office would result in an unacceptable discontinuity in service. The second change would give the NWS the option to keep hurricane and tropical storm watches and warnings in place for those systems.

Beginning 1 June, the following new NWS watch/warning definitions will go into effect:

  • Hurricane/Typhoon Warning: An announcement that sustained winds of 64 knots (74 mph or 119 km/hr) or higher are expected somewhere within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds (24 hours for the Western North Pacific). The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less than hurricane force.

  • Hurricane Watch: An announcement that sustained winds of 64 knots (74 mph or 119 km/hr) or higher are possible within the specified area in association with a tropical, subtropical, or post-tropical cyclone. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical storm force winds.

  • Tropical Storm Warning: An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are expected somewhere within the specified area within 36 hours (24 hours for the Western North Pacific) in association with a tropical, subtropical, or post-tropical cyclone.

  • Tropical Storm Watch: An announcement that sustained winds of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) are possible within the specified area within 48 hours in association with a tropical, subtropical, or post-tropical cyclone.

An example of a National Hurricane Center Public Advisory (TCP) issued for an ongoing post-tropical cyclone is given below.

Example Public Advisory

BULLETIN
POST-TROPICAL CYCLONE MANDY ADVISORY NUMBER  29
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL182020
1100 AM EDT MON OCT 29 2020
 
...MANDY LOSES TROPICAL CHARACTERISTICS BUT HURRICANE WARNINGS
REMAIN IN EFFECT...
...MANDY EXPECTED TO BRING LIFE-THREATENING STORM SURGE AND 
HURRICANE-FORCE WINDS TO THE COAST THIS AFTERNOON...
 
 
SUMMARY OF 1100 AM EDT...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...37.5N 71.5W
ABOUT 205 MI...330 KM SE OF ATLANTIC CITY NEW JERSEY
ABOUT 260 MI...415 KM SSE OF NEW YORK CITY
MAXIMUM SUSTAINED WINDS...90 MPH...150 KM/H
PRESENT MOVEMENT...NNW OR 330 DEGREES AT 18 MPH...30 KM/H
MINIMUM CENTRAL PRESSURE...943 MB...27.85 INCHES
 
 
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...
 
THE BERMUDA WEATHER SERVICE HAS DISCONTINUED THE TROPICAL STORM
WARNING FOR BERMUDA.
 
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
 
A HURRICANE WARNING IS IN EFFECT FOR...
* NORTH OF CHINCOTEAGUE VIRGINIA TO CHATHAM MASSACHUSETTS
* THE TIDAL POTOMAC FROM COBB ISLAND TO SMITH POINT
* THE MIDDLE AND UPPER CHESAPEAKE BAY AND DELAWARE BAY 

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* NORTH OF SURF CITY NORTH CAROLINA TO CHINCOTEAGUE
* PAMLICO AND ALBEMARLE SOUNDS
* NORTH OF CHATHAM TO MERRIMACK RIVER MASSACHUSETTS
* THE LOWER CHESAPEAKE BAY
 
FOR STORM INFORMATION SPECIFIC TO YOUR AREA...INCLUDING INLAND 
WATCHES AND WARNINGS...PLEASE MONITOR PRODUCTS ISSUED BY YOUR 
LOCAL NATIONAL WEATHER SERVICE FORECAST OFFICE. 
 
 
DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
SATELLITE AND RECONNAISSANCE DATA INDICATE THAT THE CIRCULATION OF 
MANDY HAS BECOME OVERTAKEN BY A COLD FRONT DURING THE PAST FEW 
HOURS...AND AS A RESULT MANDY CAN NO LONGER BE CLASSIFIED AS A 
TROPICAL CYCLONE.  HOWEVER...TO AVOID AN UNACCEPTABLE DISCONTINUITY 
IN SERVICE...THE NATIONAL HURRICANE CENTER WILL CONTINUE TO ISSUE 
ADVISORIES ON MANDY AS A POST-TROPICAL CYCLONE AS LONG AS THE SYSTEM 
POSES A SIGNIFICANT THREAT TO LIFE AND PROPERTY.  IN ADDITION...THE 
COASTAL HURRICANE AND TROPICAL STORM WARNINGS WILL REMAIN IN EFFECT.

AT 1100 AM EDT...1500 UTC...THE CENTER OF POST-TROPICAL CYCLONE MANDY 
WAS LOCATED NEAR LATITUDE 37.5 NORTH...LONGITUDE 71.5 WEST. MANDY IS
MOVING TOWARD THE NORTH-NORTHWEST NEAR 18 MPH...30 KM/H. A TURN
TOWARD THE NORTHWEST IS EXPECTED SOON...FOLLOWED BY A TURN TOWARD
THE WEST-NORTHWEST TONIGHT. ON THE FORECAST TRACK... THE CENTER OF
MANDY IS EXPECTED TO MAKE LANDFALL ALONG OR JUST SOUTH OF THE
SOUTHERN NEW JERSEY COAST THIS EVENING OR TONIGHT.
 
REPORTS FROM AN AIR FORCE HURRICANE HUNTER AIRCRAFT INDICATE THAT
THE MAXIMUM SUSTAINED WINDS HAVE INCREASED TO NEAR 90 MPH...150
KM/H...WITH HIGHER GUSTS. ALTHOUGH MANDY HAS BECOME A FRONTAL OR 
WINTERTIME LOW PRESSURE SYSTEM...THIS TRANSITION WILL NOT BE 
ACCOMPANIED BY A WEAKENING OF THE SYSTEM. IN FACT...A LITTLE 
STRENGTHENING IS POSSIBLE DURING THIS PROCESS. MANDY IS EXPECTED 
TO WEAKEN AFTER MOVING INLAND.
 
HURRICANE-FORCE WINDS EXTEND OUTWARD UP TO 175 MILES...280 KM...
MAINLY SOUTHWEST OF THE CENTER...AND TROPICAL-STORM-FORCE WINDS
EXTEND OUTWARD UP TO 485 MILES...780 KM. SUSTAINED WINDS TO
TROPICAL STORM FORCE ARE OCCURRING FROM LONG ISLAND SOUTHWARD ALONG
THE COASTS OF NEW JERSEY...DELAWARE...AND EASTERN VIRGINIA...AND
EXTEND AS FAR INLAND AS THE CENTRAL AND SOUTHERN CHESAPEAKE BAY AND
DELAWARE BAY. A WEATHERFLOW REPORT INDICATES A SUSTAINED WIND OF 53
MPH...85 KM/H...WITH A GUST TO 63 MPH...102 KM/H...HAS RECENTLY
OCCURRED ON LONG ISLAND AT EATONS NECK NEW YORK.
 
THE ESTIMATED MINIMUM CENTRAL PRESSURE RECENTLY REPORTED BY
RECONNAISSANCE AIRCRAFT WAS 943 MB...27.85 INCHES.
 
 
HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL-STORM-FORCE WINDS ARE ALREADY OCCURRING OVER 
PORTIONS OF THE MID-ATLANTIC STATES FROM NORTH CAROLINA 
NORTHWARD TO LONG ISLAND. TROPICAL-STORM-FORCE WINDS ARE EXPECTED 
TO CONTINUE TO SPREAD OVER OTHER PORTIONS OF THE MID-ATLANTIC 
COAST...NEW YORK CITY...AND SOUTHERN NEW ENGLAND TODAY.  
HURRICANE-FORCE WINDS COULD REACH THE MID-ATLANTIC 
STATES...INCLUDING NEW YORK CITY AND LONG ISLAND...BY THIS EVENING. 
WINDS AFFECTING THE UPPER FLOORS OF HIGH-RISE BUILDINGS WILL BE
SIGNIFICANTLY STRONGER THAN THOSE NEAR GROUND LEVEL.
 
STORM SURGE...THE COMBINATION OF AN EXTREMELY DANGEROUS STORM SURGE
AND THE TIDE WILL CAUSE NORMALLY DRY AREAS NEAR THE COAST TO BE
FLOODED BY RISING WATERS. THE WATER COULD REACH THE FOLLOWING
DEPTHS ABOVE GROUND IF THE PEAK SURGE OCCURS AT THE TIME OF HIGH
TIDE...
 
NC NORTH OF SURF CITY INCLUDING PAMLICO/ALBEMARLE SOUNDS...4 TO 6 FT
SE VA AND DELMARVA INCLUDING LOWER CHESAPEAKE BAY...2 TO 4 FT
UPPER AND MIDDLE CHESAPEAKE BAY...1 TO 3 FT
LONG ISLAND SOUND...RARITAN BAY...AND NEW YORK HARBOR...6 TO 11 FT
ELSEWHERE FROM OCEAN CITY MD TO THE CT/RI BORDER...4 TO 8 FT
CT/RI BORDER TO THE SOUTH SHORE OF CAPE COD INCLUDING BUZZARDS
BAY AND NARRAGANSETT BAY...3 TO 6 FT
CAPE COD TO THE MA/NH BORDER INCLUDING CAPE COD BAY...2 TO 4 FT
MA/NH BORDER TO THE U.S./CANADA BORDER...1 TO 3 FT
 
SURGE-RELATED FLOODING DEPENDS ON THE RELATIVE TIMING OF THE SURGE
AND THE TIDAL CYCLE...AND CAN VARY GREATLY OVER SHORT DISTANCES.
GIVEN THE LARGE WIND FIELD ASSOCIATED WITH MANDY...ELEVATED WATER
LEVELS COULD SPAN MULTIPLE TIDE CYCLES RESULTING IN REPEATED AND
EXTENDED PERIODS OF COASTAL AND BAYSIDE FLOODING.  IN ADDITION...
ELEVATED WATERS COULD OCCUR FAR REMOVED FROM THE CENTER OF MANDY.
THE TRANSITION OF MANDY TO A POST-TROPICAL CYCLONE WILL NOT IN ANY 
WAY LESSEN THESE IMPACTS.  FOR INFORMATION SPECIFIC TO YOUR 
AREA...PLEASE SEE PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER 
SERVICE OFFICE.
 
RAINFALL...RAINFALL TOTALS OF 3 TO 6 INCHES ARE EXPECTED OVER FAR
NORTHEASTERN NORTH CAROLINA WITH ISOLATED MAXIMUM TOTALS OF 8
INCHES POSSIBLE. RAINFALL AMOUNTS OF 4 TO 8 INCHES ARE EXPECTED
OVER PORTIONS OF THE MID ATLANTIC STATES...INCLUDING THE DELMARVA
PENINSULA...WITH ISOLATED MAXIMUM AMOUNTS OF 12 INCHES POSSIBLE.
RAINFALL AMOUNTS OF 1 TO 3 INCHES WITH ISOLATED MAXIMUM AMOUNTS OF
5 INCHES ARE POSSIBLE FROM THE SOUTHERN TIER OF NEW YORK STATE
NORTHEASTWARD THROUGH NEW ENGLAND.
 
SNOWFALL..SNOW ACCUMULATIONS OF 2 TO 3 FEET ARE EXPECTED IN THE
MOUNTAINS OF WEST VIRGINIA WITH LOCALLY HIGHER TOTALS TODAY THROUGH
WEDNESDAY. SNOWFALL OF 1 TO 2 FEET IS EXPECTED IN THE MOUNTAINS OF
SOUTHWESTERN VIRGINIA TO THE KENTUCKY BORDER...WITH 12 TO 18 INCHES
OF SNOW EXPECTED IN THE MOUNTAINS NEAR THE NORTH CAROLINA/TENNESSEE
BORDER AND IN THE MOUNTAINS OF WESTERN MARYLAND.
 
SURF...DANGEROUS SURF CONDITIONS WILL CONTINUE FROM FLORIDA THROUGH
NEW ENGLAND FOR THE NEXT COUPLE OF DAYS.
 
 
NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...200 PM EDT.
NEXT COMPLETE ADVISORY...500 PM EDT.
 
$$
FORECASTER STEWART
 
NNNN


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Page last modified: Thursday, 04-Apr-2013 15:28:51 UTC