Service Change Notice
28 February 2014
There will be two changes to the Wind Speed Probability Product in 2014:
1: The name of one of the parameters in the product will change from "Individual Probability" (IP) to "Onset Probability" (OP). This parameter is defined as the probability of the event (e.g., hurricane-force winds) beginning at a particular location 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.
2: Removal of the table that 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, etc.). This table was originally intended to help users assess the risk of different storm intensities at particular times. However, 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. Because of the likelihood of misuse for land-threatening storms, NHC and CPHC are discontinuing this table until a better procedure to estimate intensity risk can be developed.
To understand the problem, consider a storm that is forecast to be just off the coast at 72 hours. The probability that the cyclone will be at any particular intensity category at 72 hours is estimated by creating a large number of potential track and intensity scenarios, based on the latest official forecast and a climatological error distribution. If the 72-hour forecast is for the storm to be very close to land, a sizable fraction of the potential scenarios will have already encountered land by that time. For these scenarios, the expected 72-hour intensity will be much lower than what would be expected for a storm that had not yet made landfall. So even though the table accurately assesses what the intensity is likely to be at 72 hours, it grossly underestimates the likely intensity for the moment when the storm comes ashore.
ZCZC MIAPWSAT4 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISAAC WIND SPEED PROBABILITIES NUMBER 23
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
2100 UTC SUN AUG 26 2012
AT 2100Z THE CENTER OF TROPICAL STORM ISAAC WAS LOCATED NEAR
LATITUDE 24.2 NORTH...LONGITUDE 82.3 WEST WITH MAXIMUM SUSTAINED
WINDS NEAR 50 KTS...60 MPH...95 KM/H.
Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH)
ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME
EASTERN DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME
CENTRAL DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME
WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS
CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST
...34 KT (39 MPH... 63 KPH)...
...50 KT (58 MPH... 93 KPH)...
...64 KT (74 MPH...119 KPH)...
FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS
PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE
OP IS THE PROBABILITY OF THE EVENT BEGINNING DURING
AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY)
(CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN
18Z SUN AND THE FORECAST HOUR (CUMULATIVE PROBABILITY)
PROBABILITIES ARE GIVEN IN PERCENT
X INDICATES PROBABILITIES LESS THAN 1 PERCENT
PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN
THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT.
PROBABILITIES FOR 64 KT ARE SHOWN WHEN THE 5-DAY CUMULATIVE
PROBABILITY IS AT LEAST 1 PERCENT.
- - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - -
FROM FROM FROM FROM FROM FROM FROM
TIME 18Z SUN 06Z MON 18Z MON 06Z TUE 18Z TUE 18Z WED 18Z THU
PERIODS TO TO TO TO TO TO TO
06Z MON 18Z MON 06Z TUE 18Z TUE 18Z WED 18Z THU 18Z FRI
FORECAST HOUR (12) (24) (36) (48) (72) (96) (120)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
LOCATION KT
FT PIERCE FL 34 9 2(11) X(11) X(11) X(11) X(11) X(11)
W PALM BEACH 34 14 2(16) X(16) X(16) X(16) X(16) X(16)
MIAMI FL 34 99 X(99) X(99) X(99) X(99) X(99) X(99)
MARATHON FL 34 99 X(99) X(99) X(99) X(99) X(99) X(99)
MARATHON FL 50 14 X(14) X(14) X(14) X(14) X(14) X(14)
KEY WEST FL 34 99 X(99) X(99) X(99) X(99) X(99) X(99)
KEY WEST FL 50 99 X(99) X(99) X(99) X(99) X(99) X(99)
MARCO ISLAND 34 99 X(99) X(99) X(99) X(99) X(99) X(99)
FT MYERS FL 34 48 1(49) 2(51) X(51) X(51) X(51) X(51)
VENICE FL 34 37 5(42) 2(44) 1(45) X(45) 1(46) X(46)
TAMPA FL 34 18 8(26) 3(29) 2(31) X(31) 1(32) X(32)
TALLAHASSEE FL 34 X 7( 7) 10(17) 6(23) 6(29) 1(30) X(30)
ST MARKS FL 34 1 9(10) 9(19) 6(25) 5(30) 1(31) 1(32)
APALACHICOLA 34 3 11(14) 16(30) 9(39) 7(46) 1(47) X(47)
APALACHICOLA 50 X X( X) 2( 2) 2( 4) 1( 5) 1( 6) X( 6)
APALACHICOLA 64 X X( X) X( X) 1( 1) X( 1) X( 1) X( 1)
PANAMA CITY FL 34 1 11(12) 20(32) 13(45) 7(52) 1(53) 1(54)
PANAMA CITY FL 50 X X( X) 3( 3) 4( 7) 3(10) 1(11) X(11)
PANAMA CITY FL 64 X X( X) X( X) 1( 1) 1( 2) X( 2) X( 2)
COLUMBUS GA 34 X X( X) 3( 3) 6( 9) 11(20) 2(22) 1(23)
MONTGOMERY AL 34 X X( X) 7( 7) 10(17) 18(35) 3(38) 1(39)
MONTGOMERY AL 50 X X( X) X( X) X( X) 5( 5) 2( 7) X( 7)
MONTGOMERY AL 64 X X( X) X( X) X( X) 1( 1) 1( 2) X( 2)
PENSACOLA FL 34 X 6( 6) 24(30) 25(55) 14(69) 2(71) X(71)
PENSACOLA FL 50 X X( X) 2( 2) 14(16) 12(28) 1(29) 1(30)
PENSACOLA FL 64 X X( X) X( X) 4( 4) 5( 9) 2(11) X(11)
MOBILE AL 34 X 3( 3) 22(25) 31(56) 20(76) 2(78) X(78)
MOBILE AL 50 X X( X) 2( 2) 15(17) 21(38) 2(40) X(40)
MOBILE AL 64 X X( X) X( X) 3( 3) 12(15) 1(16) X(16)
GULFPORT MS 34 X 3( 3) 22(25) 33(58) 21(79) 2(81) X(81)
GULFPORT MS 50 X X( X) 2( 2) 19(21) 22(43) 2(45) X(45)
GULFPORT MS 64 X X( X) X( X) 5( 5) 13(18) 2(20) X(20)
STENNIS SC 34 X 2( 2) 19(21) 32(53) 23(76) 3(79) 1(80)
STENNIS SC 50 X X( X) 1( 1) 15(16) 22(38) 2(40) X(40)
STENNIS SC 64 X X( X) X( X) 4( 4) 12(16) 1(17) X(17)
BURAS LA 34 X 5( 5) 29(34) 33(67) 14(81) 2(83) 1(84)
BURAS LA 50 X X( X) 5( 5) 25(30) 15(45) 2(47) X(47)
BURAS LA 64 X X( X) 1( 1) 8( 9) 11(20) 1(21) X(21)
JACKSON MS 34 X X( X) 3( 3) 11(14) 33(47) 6(53) 1(54)
JACKSON MS 50 X X( X) X( X) X( X) 12(12) 4(16) X(16)
JACKSON MS 64 X X( X) X( X) X( X) 3( 3) 2( 5) X( 5)
NEW ORLEANS LA 34 X 1( 1) 16(17) 29(46) 23(69) 3(72) 1(73)
NEW ORLEANS LA 50 X X( X) 1( 1) 10(11) 18(29) 3(32) 1(33)
NEW ORLEANS LA 64 X X( X) X( X) 1( 1) 9(10) 1(11) X(11)
BATON ROUGE LA 34 X X( X) 9( 9) 18(27) 24(51) 6(57) X(57)
BATON ROUGE LA 50 X X( X) X( X) 2( 2) 14(16) 3(19) X(19)
BATON ROUGE LA 64 X X( X) X( X) X( X) 5( 5) 2( 7) X( 7)
NEW IBERIA LA 34 X X( X) 7( 7) 12(19) 20(39) 7(46) X(46)
NEW IBERIA LA 50 X X( X) X( X) 1( 1) 9(10) 2(12) 1(13)
NEW IBERIA LA 64 X X( X) X( X) X( X) 3( 3) 2( 5) X( 5)
SHREVEPORT LA 34 X X( X) X( X) 1( 1) 9(10) 6(16) 1(17)
PORT ARTHUR TX 34 X X( X) X( X) 3( 3) 10(13) 5(18) X(18)
PORT ARTHUR TX 50 X X( X) X( X) X( X) 1( 1) 2( 3) 1( 4)
PORT ARTHUR TX 64 X X( X) X( X) X( X) X( X) 1( 1) X( 1)
$$
FORECASTER PASCH
NNNN
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