## Tropical Cyclone Wind Speed Probability Text Products

Wind speed probability products are designed to answer these questions:

- What are the chances of experiencing these winds?
- When is the event most likely to start?

- Cumulative probabilities (0-12, 0-24, 0-36 etc) through 120 hours (5 days) indicate the overall likelihood that the event will
sometime in the given time period.These can be stepped through incrementally or animated on the web pages.*occur* - Specific sustained wind speed thresholds available:
- 34 knots (39 mph)Tropical Storm strength
- 50 knots (58 mph)
- 64 knots (74 mph)Hurricane strength

__What the numbers mean__

- Low probability numbers for extreme events
insignificant.*are not* - 30% probability of experiencing 64 knot winds means a roughly 1 in 3 chance of hurricane conditions
- The chance of having 34 knot winds (tropical storm conditions) will be much higher for the same storm

We welcome any and all feedback on these products. Please e-mail your comments to W-HFO.Webmaster@noaa.gov.

__How to read the Wind Probability Text Product__

These tables do not directly indicate what the wind speeds will be at any location at any time, nor do they indicate when the winds will cease.An example product is included below.

__The top section__

These are values for onset and cumulative probabilities for select land and marine locations across Hawaii and the Central Pacific.

Taking Honolulu for example, the probabilities listed are:

HONOLULU 34 41 **43**(84) 7(91) 1(92) X(92) X(92) X(**92**)

HONOLULU 50 3 **41**(44) 16(60) 1(61) X(61) X(61) X(**61**)

HONOLULU 64 X **26**(26) 17(43) 1(44) X(44) X(44) X(**44**)

The first row are the probabilities of tropical storm force winds of 34 knots (39 mph). The values in parentheses are the cumulative probability of experiencing those winds at anytime up to the time period given in the column heading.So over entire 120 hour (5 day) period, there is a 92% chance of experiencing 34 knots of wind at some time. The values not in parenthesis indicate the probability of that level of winds **beginning** during the time period in the column heading.The time most likely to see the winds begin is the second period (06z to18z Monday) with a 43% chance.

The second row indicates the probabilities of experiencing 50 knots (58 mph) or greater wind speeds. The probability is 61% that such a level of strong winds will occur sometime in the 120 hour forecast period. The most likely time for the winds to begin is again the second period, with a 41% chance.

The last row indicates the probabilities of experiencing hurricane force (64 knots or 74 mph) winds or greater. Honolulu has a 44% chance of experiencing such winds during the 120 forecast period, with the second period being the most likely time for those winds to begin with a 26% chance.

__The bottom section__

Provides similar probability values as above, except using the forecast location of the center of the storm. As you look farther down the forecast in time, overall probabilities are decreasing. For example, note the section indicating the probabilities for the forecast location point the storm at 48 hours.

48 245N 1611W 34X4( 4)24(28)33(61)8(69)X(69)X(69)

48 245N 1611W 50XX( X)6( 6)20(26)5(31)X(31)X(31)

48 245N 1611W 64XX( X)2( 2)12(14)2(16)X(16)X(16)

The storm is forecast to be a 90 knot hurricane at this time, yet there is only an overall 16% chance that the actual location we are forecasting the storm to be will have greater than 64 knots of wind and a 69% chance that winds will be tropical storm force or higher. Although this may seem contradictory at first, it is evidence of the forecast errors in location and intensity that accounts for this. The reality with hurricane forecasts is that they are not perfect. There is a chance that the storm may end up 150 miles from where we forecast it to be 2 days in advance. There is also a chance that the storm may be exactly where we forecast it to be, but have diminished to a tropical depression with winds less than 34 knots. In either case, the location would not experience strong winds, despite the forecast from 48 hours earlier. The probability forecasts take these possibilities, and 998 others into account, therefore you will never see a 99% or higher value after the first period.

As a result, do not be tricked into thinking low probabilities farther out in time really mean nothing is going to happen. Monitor each successive forecast and view how the probabilities are changing.

Example of Tropical Cyclone Wind Speed Probabilities

HURRICANE NOTREAL PROBABILITIES NUMBER 2 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI 2100Z SUN JUL 10 2005 ...THIS IS AN EXPERIMENTAL PRODUCT FOR 2005... AT 2100Z THE CENTER OF HURRICANE NOTREAL WAS LOCATED NEAR LATITUDE 18.4 NORTH...LONGITUDE 154.3 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 115 KTS...135 MPH. CHANCES OF EXPERIENCING 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 IP(CP) WHERE IP IS THE PROBABILITY OF THE EVENT BEGINNING DURING AN INdivIDUAL TIME PERIOD (INdivIDUAL 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 0.5 PERCENT LOCATIONS SHOWN WHEN THEIR TOTAL CUMULATED 5-DAY PROBABILITY IS AT LEAST 2.5 PERCENT Z INDICATES UNIVERSAL COORDINATED TIME (GREENWICH) - - - - 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 BUOY 51004 34 99 X(99) X(99) X(99) X(99) X(99) X(99) BUOY 51004 50 99 X(99) X(99) X(99) X(99) X(99) X(99) HILO 34 99 X(99) X(99) X(99) X(99) X(99) X(99) HILO 50 69 3(72) X(72) X(72) X(72) X(72) X(72) HILO 64 32 2(34) X(34) X(34) X(34) X(34) X(34) SOUTH POINT 34 99 X(99) X(99) X(99) X(99) X(99) X(99) SOUTH POINT 50 89 3(92) X(92) X(92) X(92) X(92) X(92) SOUTH POINT 64 77 4(81) X(81) X(81) X(81) X(81) X(81) KAILUA-KONA 34 99 X(99) X(99) X(99) X(99) X(99) X(99) KAILUA-KONA 50 72 15(87) X(87) X(87) X(87) X(87) X(87) KAILUA-KONA 64 50 22(72) 1(73) X(73) X(73) X(73) X(73) KAHULUI 34 99 X(99) X(99) X(99) X(99) X(99) X(99) KAHULUI 50 12 27(39) 1(40) X(40) X(40) X(40) X(40) KAHULUI 64 3 16(19) 1(20) X(20) X(20) X(20) X(20) LANAI CITY 34 99 X(99) X(99) X(99) X(99) X(99) X(99) LANAI CITY 50 10 47(57) 2(59) 1(60) X(60) X(60) X(60) LANAI CITY 64 3 32(35) 2(37) X(37) X(37) X(37) X(37) KAUNAKAKAI 34 59 30(89) 4(93) X(93) X(93) X(93) X(93) KAUNAKAKAI 50 5 41(46) 7(53) X(53) X(53) X(53) X(53) KAUNAKAKAI 64 1 27(28) 4(32) X(32) X(32) X(32) X(32) BUOY 51002 34 99 X(99) X(99) X(99) X(99) X(99) X(99) HONOLULU 34 41 43(84) 7(91) 1(92) X(92) X(92) X(92) HONOLULU 50 3 41(44) 16(60) 1(61) X(61) X(61) X(61) HONOLULU 64 X 26(26) 17(43) 1(44) X(44) X(44) X(44) LIHUE 34 11 40(51) 35(86) 4(90) X(90) X(90) X(90) LIHUE 50 X 15(15) 40(55) 7(62) 1(63) X(63) X(63) LIHUE 64 X 7( 7) 31(38) 5(43) 1(44) X(44) X(44) NIIHAU 34 6 30(36) 40(76) 8(84) 1(85) X(85) X(85) NIIHAU 50 X 6( 6) 33(39) 10(49) 1(50) X(50) X(50) NIIHAU 64 X 2( 2) 21(23) 7(30) 1(31) X(31) X(31) 20N 160W 34 11 36(47) 15(62) 2(64) X(64) X(64) X(64) 20N 160W 50 X 8( 8) 9(17) X(17) X(17) X(17) X(17) 20N 160W 64 X 2( 2) 5( 7) X( 7) X( 7) X( 7) X( 7) 25N 160W 34 X 4( 4) 20(24) 27(51) 6(57) 1(58) X(58) 25N 160W 50 X X( X) 4( 4) 13(17) 3(20) X(20) X(20) 25N 160W 64 X X( X) 1( 1) 6( 7) 2( 9) X( 9) X( 9) 30N 160W 34 X X( X) X( X) 1( 1) 5( 6) 1( 7) X( 7) BUOY 51003 34 6 13(19) 7(26) 1(27) X(27) X(27) X(27) BUOY 51003 50 X 2( 2) 1( 3) X( 3) X( 3) X( 3) X( 3) BUOY 51001 34 X 5( 5) 20(25) 24(49) 6(55) X(55) X(55) BUOY 51001 50 X X( X) 4( 4) 10(14) 2(16) X(16) X(16) BUOY 51001 64 X X( X) 1( 1) 5( 6) 1( 7) X( 7) X( 7) FR FRIG SHOALS 34 X X( X) X( X) 3( 3) 1( 4) 1( 5) X( 5) $$ FORECASTER TEST

Location | Lat/Lon |
---|---|

Niihau | 21.9°N 160.1°W |

Lihue | 21.9°N 159.3°W |

Honolulu | 21.3°N 157.9°W |

Kaunakakai | 21.1°N 157.2°W |

Kahului | 20.9°N 156.4°W |

Lanai City | 20.8°N 156.9°W |

Kailua-Kona | 19.7°N 156.0°W |

Hilo | 19.7°N 155.0°W |

South Point | 18.9°N 155.7°W |

Buoy 51001 | 23.3°N 162.2°W |

Buoy 51002 | 17.1°N 157.8°W |

Buoy 51003 | 19.1°N 160.8°W |

Buoy 51004 | 17.4°N 152.5°W |

Johnston Island | 16.7°N 169.5°W |

Midway | 28.3°N 177.6°W |

French Frigate Shoals | 23.8°N 166.3°W |

Palmyra | 5.5°N 162.0°W |

10N 145W | 10.0°N 145.0°W |

10N 160W | 10.0°N 160.0°W |

10N 175W | 10.0°N 175.0°W |

15N 145W | 15.0°N 145.0°W |

15N 160W | 15.0°N 160.0°W |

15N 175W | 15.0°N 175.0°W |

20N 145W | 20.0°N 145.0°W |

20N 175W | 20.0°N 175.0°W |

25N 145W | 25.0°N 145.0°W |

25N 160W | 25.0°N 160.0°W |

25N 175W | 25.0°N 175.0°W |

30N 145W | 20.0°N 145.0°W |

30N 160W | 30.0°N 160.0°W |

30N 175W | 30.0°N 175.0°W |

35N 145W | 35.0°N 145.0°W |

35N 160W | 35.0°N 160.0°W |

35N 175W | 35.0°N 175.0°W |