Originally posted by NHC's Wilma Report
In the span of just 24 hours, Wilma had intensified from a 60-kt tropical storm to a 150-kt category 5 hurricane, an unprecedented event for an Atlantic tropical cyclone. It is fortunate that this ultra-rapid strengthening took place over open waters, apparently void of watercraft, and not just prior to a landfall. Wilma reached its peak sustained wind speed of 160 kt at around 1200 UTC 19 October. During the strengthening episode, Air Force reconnaissance observations indicated that the eye of the hurricane contracted to a diameter of 2 n mi; this is the smallest eye known to National Hurricane Center (NHC) staff. The estimated minimum central pressure at the time of peak intensity is 882 mb, which is a new record low value for a hurricane in the Atlantic basin. Indeed, the actual minimum pressure may well have been lower than this value, as noted in the following section.
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Highest winds measured by the AFRES were 168 kt at a flight level of 700 mb in the southeastern eyewall at 0610 UTC 19 October, when Wilma was over the northwestern Caribbean Sea. Using a standard eyewall reduction factor (ratio of surface to flight level winds of 0.9) yields a surface wind of 151 kt. Since the central pressure was still falling at the time of the last pass of the aircraft through the eye at around 0800 UTC, it is likely that the winds also increased some more from 0800 to 1200 UTC. Therefore the peak intensity of Wilma is estimated to be 160 kt at 1200 UTC 19 October.
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Wilma’s deepening rate over the northwestern Caribbean Sea, from late on 18 October to early on 19 October, was incredible. Over the period from 2310 UTC to 0433 UTC, the central pressure fell from 954 mb to 901 mb, which is a deepening rate of 9.9 mb per hour. The minimum central pressure measured by dropsonde was 884 mb at 0801 UTC 19 October. Surface winds from this dropsonde were measured to be 23 kt, so the dropsonde probably did not capture the lowest pressure in Wilma’s eye. Therefore the pressure around 0800 UTC was probably a couple of mb lower than 884, estimated at 882 mb. This is the lowest central pressure in the NHC records for the Atlantic basin. Given that the pressure was still falling at this time, it is possible that the pressure then dropped a little below 882 mb. It should be added that the largest 6-, 12-, and 24-h drops in best track central pressure for Wilma, 54 mb from 0000 to 0600 UTC 19 October, 83 mb from 1800 UTC 18 October to 0600 UTC 19 October, and 97 mb from 1200 UTC 18 October to 1200 UTC 19 October, respectively, are by far the largest in the available records for these periods going back to 1851. The previous record 6-h deepening was 38 mb in Hurricane Beulah, September 1967, the previous record 12-h deepening was 48 mb in Hurricane Allen, August 1980, and the previous record 24-h deepening was 72 mb in Hurricane Gilbert, September 1988.
