NOUS41 KWBC 051500

PNSWSH

 

Public Information Statement 17-22

National Weather Service Headquarters Silver Spring MD

1100 AM EDT Fri May 5 2017

 

To:       Subscribers:

          -NOAA Weather Wire Service

          -Emergency Managers Weather Information Network

          -NOAAPORT

          Other NWS Partners and NWS Employees

 

From:     Allison Allen

          Chief, Marine, Tropical and Tsunami Services Branch

 

Subject:  Soliciting comments on an experimental Arrival of     

          Tropical-Storm-Force Winds Graphic through 

          November 30, 2017

 

Effective May 15, 2017 and continuing through November 30, 2017,

NWS is seeking user feedback on an experimental Arrival of

Tropical-Storm-Force Winds Graphic issued by the National

Hurricane Center (NHC).

 

The anticipated arrival of sustained tropical-storm-force winds

from a tropical cyclone is a critical threshold for coastal

communities. For example, emergency managers use this

information to help determine when to begin and complete coastal

evacuations, while members of the public need to know when to

prepare their homes or businesses. Once sustained tropical-

storm-force winds begin, such preparations usually become too

dangerous or difficult. 

 

Historically, many decision makers have inferred the arrival of

sustained tropical-storm-force winds from NHC products

deterministically, without accounting for tropical cyclone track

or size uncertainty. The risk in not factoring in these elements

of uncertainty is that communities may have less time to prepare

if a tropical cyclone speeds up or increases in size beyond

NHC’s initial forecasts. 

 

To better meet users' needs, NHC has developed a set of

prototype graphics that depict when sustained tropical-storm-

force winds from an approaching tropical cyclone could arrive at

individual locations. The prototype maps were developed and

tested using social science techniques, including one-on-one

telephone interviews, focus groups, and surveys with emergency

managers, broadcast meteorologists, and NWS meteorologists to

gather opinions on the idea, content, and design of the

products.

 

NHC creates the prototype timing graphics using the same Monte

Carlo wind speed probability model currently used to determine

the risk of tropical-storm- and hurricane-force winds at

individual locations. This model constructs 1,000 plausible

scenarios using the official NHC tropical cyclone forecast and

its historical errors. Additional information on this product

and the underlying technique are online at:

 

http://www.nhc.noaa.gov/about/pdf/About_Windspeed_Probabilities.pdf

 

NHC will have two thresholds for producing the experimental

Arrival of Tropical-Storm-Force Winds Graphic and posting it on

the NHC website for all tropical cyclones, post-tropical

cyclones, and potential tropical cyclones for which NHC is

issuing advisories:

 

1. Earliest Reasonable Arrival Time: This graphic identifies

   the time window that users at individual locations can

   safely assume will be free from tropical-storm-force winds. 

   Specifically, this is the time before which there is no

   more than a 1-in-10 (10 percent) chance of seeing the onset

   of sustained tropical-storm-force winds. This is when

   preparations should ideally be completed for those with a low

   tolerance for risk.

 

2. Most Likely Arrival Time: This graphic identifies the time

   before or after which the onset of tropical-storm-force

   winds is equally likely. This graphic would be more

   appropriate for users who are willing to risk not having

   completed all their preparations before the storm arrives.

 

Timing information will only be available for locations that

have at least a 5 percent chance of experiencing sustained

tropical-storm-force winds during the next 5 days.

 

Each of these thresholds will also be available overlaid on top

of the cumulative 5-day probability of tropical-storm-force

winds, providing a single combined depiction of the likelihood

of tropical-storm-force winds at individual locations, along

with their possible or likely arrival times.

 

The graphics will be updated with each new NHC full advisory

package. Arrival times will be depicted with higher temporal

resolution (i.e., in 6-hour intervals) during the first day of

the 5-day forecast, increasing to lower temporal resolution

(i.e., in 12-hour intervals) after the first day of the 5-day

forecast period.  Arrival times will be referenced to 8 AM and 8

PM local time, using a constant time zone that corresponds to

where the cyclone is located at the time of the advisory.  For

example, if a cyclone is located in the Eastern Time Zone at the

time of an advisory but is forecast to move into the Central

Time Zone during the 5-day forecast period; all times on the

graphic will be referenced to the Eastern Time Zone.

 

When NHC is issuing advisories, the default graphic will be

available as a clickable thumbnail within the storm window box

for active cyclones on the NHC main webpage (www.nhc.noaa.gov). 

After clicking on the thumbnail, users can select any of the

four options.

 

Additional information and map examples are online at:

 

www.hurricanes.gov/experimental/arrivaltimes/

 

Users are encouraged to provide feedback on this experimental

product by using the brief survey and comment form available

online at:

 

http://www.nws.noaa.gov/survey/nws-survey.php?code=ARRIVALTSFW

 

For technical questions regarding this notice, please contact:

 

James Franklin

Chief, Hurricane Specialist Unit

National Hurricane Center

Miami, FL  33165

Telephone: 305-229-4475

Email: James.Franklin@noaa.gov

 

For policy questions regarding this notice, please contact:

 

Jessica Schauer

NWS Marine, Tropical and Tsunami Services Branch

Miami, FL  33165

Telephone: 305-229-4476

Email: Jessica.Schauer@noaa.gov

 

National Public Information Statements are online at:

 

http://www.nws.noaa.gov/os/notif.htm

 

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