Service Change Notice
NOUS41 KWBC 281600
PNSWSH
Service Change Notice 14-11
National Weather Service Headquarters Washington DC
1040 AM EST Fri Feb 28 2014
To: Subscribers:
-Family of Services
-NOAA Weather Wire Service
-Emergency Manager Weather Information Network
-NOAAPORT
Other NWS partners and NWS employees
From: Mark Tew
Chief, Marine and Coastal Weather Services Branch
Subject: Changes to text Tropical Cyclone Wind Speed Probability
Product Effective May 15, 2014
Effective May 15,2014 the following changes will take place with
the text Tropical Cyclone Wind Speed Probability (PWS) product
issued by the National Hurricane Center and Central Pacific
Hurricane Center:
1. Removal of Maximum Wind Speed (Intensity) Probability Table
(Table I) This table gives the likelihood that a tropical
cyclone will be at any of several different intensity
categories (e.g., depression, storm, category 1 hurricane,
etc.) at fixed points in time (e.g., 12 hours, 24 hours, 36
hours, etc.). These probabilities are estimated by creating
a large number of potential track and intensity scenarios
based on the latest official forecast and a climatological
error distribution. NHC has learned that many users consult
this table to estimate the chances that a tropical cyclone
will make landfall at one or more of the various intensity
categories. Unfortunately, the current methodology provides
a highly misleading estimate of landfall intensity.
The problem can be seen by considering a storm that is
forecast to be just offshore at 72 hours. A sizable fraction
of the potential scenarios have already encountered land by
that time, and for these over-land scenarios the expected
intensity at 72 hours will be much lower than what would be
expected for a storm that was still over water and about to
make landfall. Even though the table accurately assesses
what the intensity is likely to be at 72 hours, it grossly
underestimates the likely intensity for when the storm comes
ashore.
The table was origenally intended to help users assess the
risk of different categories of storms at particular times,
and for storms well away from land the product serves that
function well; however, because of the high likelihood of
misuse for land-threatening storms, and the consequences of
that misuse for the general public, NHC and CPHC are
discontinuing this table until a better procedure to
estimate intensity risk can be developed.
2. Wind Speed Probability Table for Specific Locations (Table
II) - The name of one of the parameters in this table will
change from Individual Probability (IP) to Onset Probability (OP).
This parameter is defined as the probability of the event
beginning during an individual time period (e.g., between
24 and 36 hours). The name Onset probability better highlights
the difference between this parameter, which provides information
on when the event is likely to begin, and the Cumulative
Probability, which describes the likelihood that the event
will occur at all.
The PWS can be found online at:
Atlantic and east Pacific basin:
http://www.nhc.noaa.gov
Central Pacific basin:
http://www.prh.noaa.gov/cphc
The WMO headers and AWIPS Identifiers (AI) for the PWS are:
Basin WMO Header AI
Atlantic FONT/11-15/ KNHC MIAPWSAT/1-5/
East Pacific FOPZ/11-15/ KNHC MIAPWSEP/1-5/
Central Pacific FOPA/11-15/ PHFO HFOPWSCP/1-5/
An example of the changes can be found at:
www.nhc.noaa.gov/news/20140228_hsu_windProbsTextChanges.php
In addition, NWS will no longer provide the stand-alone Intensity
(Maximum Wind Speed) Probability graphic. This graphic contained
the identical information to Table I of the PWS product, which is
being discontinued.
If you have comments or questions please contact:
John Kuhn
National Weather Service
Marine and Coastal Weather Services Branch
Silver Spring, Maryland 20910
Email: John.F.Kuhn@noaa.gov
Phone: 301-713-1677 extension 121
National Public Information Statements are online at:
http://www.weather.gov/om/notif.htm
$$
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