NOUS41 KWBC 011848
PNSWSH
Public
Information Statement
National Weather
Service Headquarters Washington DC
148 PM EST Thu
Mar 1 2012
To: Subscribers:
-Family of Services
-NOAA Weather Wire Service
-Emergency Managers Weather
Information Network
-NOAAPORT
Other NWS partners and NWS employees
From: Mark Tew
Chief, Marine and Coastal Services
Branch
Subject: Minor
Modification of Saffir-Simpson Hurricane Wind
Scale Thresholds Effective May 15,
2012
Effective May 15,
2012, the Saffir-Simpson Hurricane Wind Scale
(SSHWS) will be
adjusted slightly to resolve issues associated
with the conversion of units used for wind speed.
This change
follows a public comment period conducted in
2011.
The National
Hurricane Center (NHC) and Central Pacific Hurricane
(CPHC) assign
intensities of hurricanes in 5-knot (kt)
increments. For advisory products, these intensities
are
converted to miles per hour (mph) and kilometers per
hour (km/h),
and then rounded to the nearest 5-mph or 5-km/h
increments.
Challenges occur
when the current Category 4 intensity is 115 kt
(132.3
mph). Although 115 kt is within the Category 4 range, the
equivalent rounded wind speed in mph is 130 mph, which
is in the
Category
3 range. To classify the
hurricane as a Category 4 in
both sets of units (kt
and mph), NHC and CPHC must incorrectly
convert 115 kt to 135 mph
in the advisory products. A similar
issue occurs when the current Category 4 intensity
of 135 kt is
converted to km/h.
Effective May 15,
2012, to resolve these rounding issues,
Category 4 on the
SSHWS will be broadened by one mph at each end
of the range, yielding a new range of 130-156
mph. This will
also result in a minor modification of the
Category 3 and 5 wind
speed thresholds. The SSHWS will change as
follows:
From:
Category 3:
111-130 mph (96-113 kt, 178-209 km/h)
Category 4:
131-155 mph (114-135 kt, 210-249 km/h)
Category 5: 156
mph or higher (136 kt or higher, 250 km/h or
higher)
To:
Category 3:
111-129 mph (96-112 kt, 178-208 km/h)
Category 4:
130-156 mph (113-136 kt, 209-251 km/h)
Category 5: 157
mph or higher (137 kt or higher, 252 km/h or
higher)
There will be no
change to the wind speeds currently assigned to
Categories
1 and 2.
With this change,
a 115-kt Category 4 hurricane will have its
intensity properly converted to mph and rounded to the
nearest 5
mph (130 mph) and remain within the Category 4
mph range.
Important
note: Since intensities are assigned
using 5-kt
increments, neither storms in the historical record nor
any
future storms will have their SSHWS category
changed as a result
of this modification to the scale.
The NWS wishes to
remind media, partners, and the public the
Saffir-Simpson Hurricane Wind Scale provides
information on wind
impacts only.
The scale does not provide commentary or
information on other impacts or characteristics of
tropical
cyclones.
Additional
information on this change can be found at:
http://www.nhc.noaa.gov/aboutsshws.php
If you have any
questions, please contact
John Kuhn
National Weather Service
Silver Spring, Maryland 20910
301 713 1677 ext. 121
john.f.kuhn@noaa.gov
National Public
Information Notices are online at:
http://www.nws.noaa.gov/om/notif.htm
$$