Hurricane Allen - Meteorological History

Meteorological History

Allen was an early Cape Verde-type hurricane which originated from a tropical wave that previously moved off the African coastline on July 30. The system developed as it moved westward, becoming a tropical depression on August 1. However, the National Hurricane Center did not initiate advisories on Allen until almost 24 hours later, while centered 1,300 mi (2,100 km) east of the Windward Islands. Early on August 2, as the depression moved towards the Caribbean, it had intensified, and became the first named storm of the season. The National Hurricane Center noted that conditions appeared favorable for further intensification. However, it was also noted that a large cold-low north of Puerto Rico was producing strong westerly wind shear, which would cause Allen to possibly encounter unfavorable conditions within 72 hours. Although slower forward movement was anticipated, Allen kept at generally the same westward pace between 17 and 23 mph (27 and 37 km/h). By August 3, the National Hurricane Center retracted predictions of less favorable conditions from the cold-low north of Puerto Rico, since that weather system was weakening and moving westward.

At 1600 UTC on August 3, the National Hurricane Center upgraded Allen to hurricane status, as an Air Force Plane recorded winds of 100 mph (155 km/h). However, in post-analysis, it was discovered that Allen had been a hurricane since 0000 UTC on August 3. Shortly after the upgrade, Allen began a period of rapid deepening, and intensified into a major hurricane at 0000 UTC August 4, while roughly 38 mi (61 km) northwest of Bridgetown, Barbados. Six hours later, Allen passed only 8 mi (13 km) south of St. Lucia at 0600 UTC. Although the National Hurricane Center noted that conditions favored slow strengthening, Allen continued to rapidly intensify, and became a Category 4 hurricane only two hours after that advisory. Later on August 4, the National Hurricane Center noted a barometric pressure of 946 mbar (946 hPa; 27.9 inHg), and that the it would not drop significantly within 24 hours. Shortly before 0000 UTC on August 5, the minimum pressure decreased to 924 mbar (924 hPa; 27.3 inHg), which was noted as equivalent to Hurricane David in the previous season.

By August 5, Allen intensified into a Category 5 hurricane during while south of Puerto Rico. This made Allen the earliest Category 5 hurricane in the Atlantic on record, but was later surpassed by Hurricane Emily which reached that intensity on July 16, 2005. During this time, Allen attained a central pressure of 911 mbar (911 hPa; 26.9 inHg), the lowest pressure on record in the eastern Caribbean sea. Hence, the barometric pressure dropped by 35 mbar (35 hPa; 1.0 inHg) less than 10 hours after the National Hurricane Center stated that the pressure would not decrease significantly within 24 hours.

The eye passed between Hispaniola and Jamaica as a Category 4 hurricane. After weakening due to friction with the mountains of Haiti and Jamaica, Allen intensified back to a Category 5 hurricane, retaining this intensity for over a day. The storm moved between Cuba and the Yucatán Peninsula, reaching its minimum pressure of 899 mbar (899 hPa; 26.5 inHg) while crossing the Yucatán Channel. During Allen's trek through the Caribbean Sea and the Gulf of Mexico, its center of circulation never crossed over land despite its close passage to various islands in and around the Caribbean sea.

Allen again weakened to a Category 4 storm due to friction with Mexico, but restrengthened into a Category 5 hurricane for a third time as it moved over the open waters of the Gulf of Mexico, keeping this intensity for nearly a full day and with a pressure drop to 909 mbar (909 hPa; 26.8 inHg), the lowest pressure ever recorded in the western Gulf of Mexico. Shortly before landfall, a dry air mass in the western Gulf of Mexico caused the storm to weaken substantially. Allen made landfall north of Brownsville, Texas as a Category 3 storm with maximum sustained winds of 115 mph (185 km/h). Allen became extratropical on August 11.