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NOUS41 KBOX 281624
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MAZ020>023-RIZ005>007-291630-

SERVICE CHANGE NOTICE
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
1124 AM EST THU JAN 28 2021

TO:        SUBSCRIBERS:
           -NOAA WEATHER WIRE SERVICE
           -EMERGENCY MANAGERS WEATHER INFORMATION NETWORK
           -NOAAPORT
           OTHER NWS PARTNERS, USERS AND EMPLOYEES

FROM:      ANDY NASH
           METEOROLOGIST-IN-CHARGE
           WEATHER FORECAST OFFICE BOSTON/NORTON MA

SUBJECT:   CHANGES IN GAGE REPORTING, FORECASTS AND FLOOD
           CATEGORIES FOR THE TIDE GAGE NEW BEDFORD HURRICANE
           BARRIER AT BUZZARDS BAY /NBDM3/

NWS BOSTON/NORTON MA ANNOUNCES AN UPDATE TO TIDE GAGE DATA
DISPLAY, FLOOD CATEGORIES AND TOTAL WATER LEVEL FORECASTS FOR THE
ADVANCED HYDROLOGIC PREDICTION SERVICE (AHPS) SITE NEW BEDFORD
HURRICANE BARRIER AT BUZZARDS BAY, MA. THIS CHANGE WILL TAKE PLACE
ON MARCH 2, 2021. 

THE TIDE GAGE AT NEW BEDFORD HURRICANE BARRIER IS OWNED AND 
OPERATED BY THE U.S. ARMY CORPS OF ENGINEERS. TOTAL WATER LEVEL 
(TWL) FORECASTS, CONSISTING OF ASTRONOMICAL TIDE PLUS SURGE, ARE 
ISSUED AT THIS LOCATION A MINIMUM OF TWICE DAILY BY NWS 
BOSTON/NORTON MA. DATA AND TWL FORECASTS ARE DISPLAYED ON THE 
FOLLOWING WEB PAGE:

HTTPS://WATER.WEATHER.GOV/AHPS2/HYDROGRAPH.PHP?WFO=BOX&GAGE=NBDM3

REAL-TIME WATER ELEVATION DATA ARE TRANSMITTED RELATIVE TO THE
LAND-BASED DATUM OF NGVD29. TO REMAIN CONSISTENT WITH OTHER TIDE
GAGES IN MA AND RI WHERE NWS BOSTON/NORTON PROVIDES TWL FORECASTS,
WATER LEVEL OBSERVATIONS AND TWL FORECASTS ARE DISPLAYED RELATIVE
TO MEAN LOWER LOW WATER (MLLW).

WHEN THE NEW BEDFORD AHPS PAGE WAS CREATED, THE CONVERSION FROM
NGVD29 TO MLLW FOR THIS SITE WAS +1.5 FEET. THIS LEGACY
CONVERSION IS STILL BEING USED AT THIS TIME. HOWEVER MORE 
RECENTLY, THE U.S. ARMY CORPS OF ENGINEERS, IN COORDINATION WITH 
NOAA/NATIONAL OCEAN SERVICE, HAS ADOPTED AN UPDATED CONVERSION OF 
NGVD29 STAGE + 1.14 FEET TO CONVERT TO MLLW. THIS UPDATED 
CONVERSION MATCHES THE NEW BEDFORD TIDE GAGE DATA WITH THE 
NOAA/NOS ASTRONOMICAL TIDE TABLE FOR NEW BEDFORD, CLARKS POINT MA.

NWS BOSTON/NORTON ANNOUNCES THAT EFFECTIVE 1700 COORDINATED
UNIVERSAL TIME, TUESDAY MARCH 2 2021, NWS BOSTON/NORTON WILL
ADJUST ITS DISPLAYED DATA AND FORECASTS TO UTILIZE THE UPDATED
DATUM CONVERSION TO MLLW.

TO ENSURE CONSISTENCY IN NWS FORECAST AND WARNING SERVICES, THIS
CHANGE REQUIRES AN ADJUSTMENT TO FLOOD CATEGORY VALUES FOR THE
NEW BEDFORD HURRICANE BARRIER TIDE GAGE. THE NEW FLOOD CATEGORY 
VALUES WILL BE AS FOLLOWS:

1. NEW ACTION STAGE IS 5.5 FEET. LEGACY ACTION STAGE IS 6.0 FEET.
2. NEW FLOOD STAGE IS 6.0 FEET. LEGACY FLOOD STAGE IS 6.5 FEET.
3. NEW MODERATE FLOOD STAGE IS 7.5 FEET. LEGACY MODERATE FLOOD
   STAGE IS 8 FEET.
4. NEW MAJOR FLOOD STAGE IS 9.5 FEET. LEGACY MAJOR FLOOD STAGE IS
   10 FEET.

AS PART OF THIS UPDATE, NWS BOSTON/NORTON WILL ALSO UPDATE THE
CREST HISTORY TO REFLECT THE NEW DATUM CONVERSION.

IF YOU HAVE ANY QUESTIONS OR COMMENTS ON THIS CHANGE, PLEASE
CONTACT:

NICOLE M. BELK
SENIOR SERVICE HYDROLOGIST
NATIONAL WEATHER SERVICE FORECAST OFFICE
46 COMMERCE WAY, NORTON MA 02766
PHONE: 508-622-3250
E-MAIL: NICOLE.BELK@NOAA.GOV

$$

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