for National Geographic News
The 2005 hurricane season reached two more milestones this week: Hurricane Wilma has become the 21st tropical storm of the season and has quickly grown into the most powerful hurricane on record in the Atlantic Basin.
The storm is expected to make landfall in the U.S. late Saturday on the southwest coast of Florida. Evacuation orders have been issued for Monroe County, which includes the Florida Keys.
State parks in the Keys have been closed to encourage tourists to leave the islands, and an evacuation order for residents goes into effect tomorrow.
Also, patients in Keys hospitals are being airlifted out of the islands.
One of the best indicators of a hurricane's intensity is its barometric pressure; very powerful hurricanes have very low readings. As of 11 a.m. Eastern time today Wilma's barometric pressure reading had dropped to 26.04 inches or 882 millibars, a record low.
Forecasters expect Wilma to lose some of its intensity before landfall, but the storm is still expected to come ashore as a major hurricane, with winds of at least 111 miles an hour (180 kilometers an hour).
The previous record for the Atlantic Basin was Hurricane Gilbert in 1988, which had a low pressure of 26.18 inches or 888 millibars. Gilbert made landfall at Mexico's Yucatán Peninsula.
The most intense hurricane to make landfall in the U.S. was the Labor Day hurricane of 1935, which had a reading of 26.35 inches or 892 millibars, when it struck the Florida Keys.
Wilma began on October 15 as a tropical depression in the central Caribbean Sea. When it became a tropical storm two days later, it was the 21st of the season. The last time that many tropical storms formed in a single season was 1933.
Wilma has astonished meteorologists with its rapid intensification. As of 4 p.m. Tuesday, Wilma was a minimal hurricane with winds of 80 miles an hour (130 kilometers an hour). But only 18 hours later it had mushroomed into the Atlantic's most powerful storm.
James Franklin, a hurricane specialist at the National Hurricane Center in Miami, said Wilma "obliterated by a wide margin" the previous record for rapid intensification set in 1967.
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