Re: Chris, Chucky & Jac
Posted by
Chris in Tampa on 9/1/2009, 12:19 am
They released the 11PM already. They public advisory is in local time "8:00 PM PDT Mon Aug 31" which is 11PM EDT.
Or do you mean you are waiting for the 1100 PM PDT (2AM EDT)?
The scale is based on knots. The problems with rounding come in when converting to miles per hour.
Category 1 Hurricane - 64-82 kt
Category 2 Hurricane - 83-95 kt
Category 3 Hurricane - 96-113 kt
Category 4 Hurricane - 114-135 kt
Category 5 Hurricane - 135+ kt
Advisory and best track speeds are in increments of 5. So a 135 knot hurricane is a cat 4 and a 140 knot hurricane is a cat 5. There is no inbetween. For example, if the hurricane hunters found 136 knot wind speeds, maybe they would round up to 140 knots in the advisory, but they might try to determine if they missed the highest winds. (not exactly sure how they determine that) But not using advisory speeds, simply using actual speeds, I'm not sure what the cutoff is.
What is a 135.1 knot storm?
What is a 135.3 knot storm?
What is a 135.5 knot storm?
Most do not get that specific with wind speed though. They round and report it to a whole number. Then the NHC keeps is simple and move up or down to an increment of 5.
For this storm here was what they did...
For this specific storm the SFMR estimated 10 second surface wind gusts to be about 132 knots at the highest point. They rounded up to 135 knots. There is a few things they could use to substantiate that, such as they may have missed the highest wind. The standard reduction factor of 90% for surface winds in comparison to flight level winds, which is a rough estimate, yields about 134 knots. Highest max winds in the NE quad is where you expect them given this storms motion. (right front quadrant is the NE quadrant in this storm) Given the storm movement of 9 kts and the SW quadrant SFMR estimated 10 second surface wind gusts of about 125 knots, you could, depending on where the two readings were in relation to each other, add up to 9 knots to that and get 134 knots. All below the threshold. Additionally, those SFMR readings are gusts, not 1 minute sustained winds. Even the flight level winds are 30 second averages. But, they usually seem to go with SFMR (if the estimates from the instrument seem valid) and estimate that to be the 1 minute sustained winds. |
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8/31/2009, 11:48 pm Post A Reply
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