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1758

MONTHLY WEA

an 850-mb flight-level wind speed of 46 kt at 1116 UTC, along with a 997-mb surface pressure. Data buoy 42036, located in the northeastern Gulf of Mexico, reported a 10-min mean wind speed of 45 kt with a gust to 64 kt at 1720 UTC on the same day. This buoy also reported a surface pressure of 1001.7 mb at 1750 UTC. Henri was centered about 25 n mi east-southeast of the buoy at the time of the 45-kt wind speed. Based on these reports, Henris highest 1-min wind speed is estimated to be 50 kt at 1800 UTC. The highest subjective Dvorak wind speed estimates were 5565 kt.

Henris rain affected much of Florida. There were 125250 mm of rain in portions of Charlotte County. There was minor freshwater flooding in two areas: from Sarasota through Lee Counties, and a small portion of southern Hernando and extreme northern Pasco County. In southern Florida and in the Florida pan- handle, rainfall totals were generally less than 50 mm. There were no deaths attributed to Henri and damage from flooding was generally minor.

Tropical storm warnings were issued for the north- western Gulf Coast of Florida as soon as a tropical depression formed. This was about 60 h before landfall, as Henri moved eastward even slower than forecast. However, winds over land never reached tropical storm force as Henri weakened to a depression before land- fall.

i. Hurricane Isabel, 619 September

Isabel was a long-lived Cape Verde hurricane that reached category-5 status on the SaffirSimpson hurri- cane scale. The intensity was category 3 or higher for 8 days, category 4 or higher for over 5 days, and category 5 or higher for over 3 days, as Isabel moved across the western North Atlantic Ocean. It made landfall near Drum Inlet on the Outer Banks of North Carolina as a category-2 hurricane. Isabel is one of the most signifi- cant tropical cyclones to affect northeastern North Carolina and east-central Virginia since Hurricane Ha- zel in 1954 and the ChesapeakePotomac Hurricane of 1933.

1) SYNOPTIC HISTORY

Isabel formed from a tropical wave that moved west- ward across the coast of Africa on 1 September. The wave moved slowly westward and gradually became better organized. By 0000 UTC 5 September, there was sufficient organized convection for satellite-based Dvorak subjective intensity estimates to begin. Devel- opment continued, and it is estimated that a tropical depression formed at 0000 UTC 6 September. The de- pression became Tropical Storm Isabel 6 h later.

THER REVIEW

VOLUME 133

Isabel turned west-northwestward on 7 September and intensified into a hurricane. Isabel turned westward on 10 September and maintained this motion until 13 September on the south side of the AzoresBermuda high pressure ridge. Isabel strengthened to a category-5 hurricane on 11 September with maximum sustained winds estimated at 145 kt at 1800 UTC that day. After this peak, the maximum winds remained in the 130140-kt range until 15 September. During this period, Isabel displayed a persistent 3545 n mi diameter eye. Figure 4 is a visible satellite image of Isabel on 12 Sep- tember, when winds were estimated at 140 kt. Isabel approached a weakness in the western portion of the AzoresBermuda high, which allowed the hurricane to turn west-northwestward on 13 September, northwest- ward on 15 September, and north-northwestward on 16 September

Increased vertical wind shear on 15 September caused Isabel to weaken. The system weakened below major hurricane status on 16 September. It maintained category-2 status with 8590-kt maximum winds for the next two days while the overall size of the hurricane increased. Isabel made landfall near Drum Inlet, North Carolina, near 1700 UTC 18 September as a category-2 hurricane, then weakened as it moved across eastern North Carolina. It weakened to a tropical storm over southern Virginia, then became extratropical as it moved across western Pennsylvania on 19 September. Isabel then moved northward and was absorbed by a larger baroclinic system moving eastward across south- central Canada.

2) METEOROLOGICAL STATISTICS

The highest winds measured by reconnaissance air- craft were 158 kt at 700-mb flight level and 157 kt at 2560 m between 1700 and 1730 UTC 13 September. A 156-kt 700-mb wind was observed at 1719 UTC 12 Sep- tember. Stronger winds were observed from GPS drop- sondes in the eyewall, with a maximum of 203 kt re- ported at 806 mb (1372 m) at 1753 UTC 13 September. This is the strongest wind ever observed in an Atlantic hurricane.

Aircraft data on 12 September indicate that Isabel had winds near 140 kt. However, the maximum inten- sity based on satellite imagery was reached on 11 Sep- tember before the first reconnaissance mission, and the satellite signature was less impressive at the time of the first mission. The maximum intensity estimate of 145 kt on 11 September is based on the aircraft data of 12 September and the satellite signature on the previous day. The minimum central pressure estimate of 915 mb on 11 September is based on similar reasoning.

The estimate of the maximum 1-min surface wind

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