Hurricane Allen was the most powerful Atlantic hurricane by wind speed on record. The second tropical depression and first named storm of the 1980 Atlantic hurricane season, Allen was also the seventh most intense Atlantic hurricane on record in terms of barometric pressure. It was one of the few hurricanes to reach Category 5 status on the Saffir–Simpson scale on three occasions, and spent more time at Category 5 status than all but two other Atlantic hurricanes. Allen is the only hurricane in the recorded history of the Atlantic basin to achieve sustained winds of 190 mph (305 km/h), and until Hurricane Patricia in 2015, these were also the highest sustained winds in the Western Hemisphere. Hurricane Allen was also the third most powerful tropical cyclone to exist in the Gulf of Mexico in terms of pressure, behind hurricanes Milton in 2024 and Rita in 2005.

Throughout its track, Allen moved through the deep tropics on a westward to northwestward course across the tropical Atlantic Ocean, Caribbean Sea, and Gulf of Mexico before making its final landfall near the United States–Mexico border. At peak strength, the hurricane passed near Haiti, causing hundreds of deaths and heavy damage. After crossing the Gulf of Mexico, Allen weakened as it struck the lower Texas coast, causing high winds, a significant storm surge, and heavy rainfall, which resulted in considerable damage to South Texas. Overall, Allen killed at least 281 people and left $1.57 billion in damages (1980 US dollars), mostly in Haiti and the United States. Due to the hurricane's impact, the name Allen was retired from the six-year revolving list of Atlantic tropical cyclone names in 1981 and replaced by Andrew. The remnants of the storm caused a brief lapse in the heat wave of 1980 in places like Dallas/Fort Worth, Texas, which had recorded 69 days of 100 °F (38 °C) heat.

Allen was an early-season Cape Verde-type hurricane, originating from a tropical wave that left the African coastline on July 30. The system developed quickly as it moved westward, becoming a tropical depression the following day. However, the National Hurricane Center did not initiate advisories on Allen until almost 24 hours later, when it was centered 1,300 mi (2,100 km) east of the Windward Islands. Early on August 2, as the depression moved quickly westward towards the Caribbean, it intensified into the first named storm of the 1980 Atlantic hurricane season. Allen rapidly strengthened as it continued westward. By the time an aircraft reconnaissance plane entered the tropical cyclone's center late on August 3, it had already achieved major hurricane status, with maximum sustained winds of 125 mph (200 km/h) and a minimum central pressure of 967 mbar (28.6 inHg), making Allen a Category 3 hurricane. The storm's central pressure dropped to 951 mbar (28.1 inHg) that night as its eye passed north of Barbados on August 4.

Allen continued to move quickly westward and entered the Caribbean Sea shortly after passing south of St. Lucia. Allen's rapid intensification continued during this time, as it was steered by a mid- to upper-level ridge to its north. Shortly before 0000 UTC on August 5, the hurricane's minimum pressure decreased to 924 mbar (924 hPa; 27.3 inHg), which was noted as equivalent to Hurricane David in the previous season. Another reconnaissance aircraft shortly thereafter discovered Allen had become an extremely strong Category 5 hurricane, with sustained winds of 180 mph (290 km/h) and a minimum pressure of 911 mbar (26.9 inHg) the following day. This was the lowest central pressure ever recorded in the eastern Caribbean Sea. Allen maintained its extreme intensity for most of the day. However, late on August 5, the storm began to weaken as it underwent an eyewall replacement cycle and interacted with the mountainous terrain of Hispaniola, with the storm taking a northwestward jog south of the island, a common track deviation for most hurricanes that have passed through the area.

Allen resumed a more westward course as it left behind Hispaniola and passed north of Jamaica and the Cayman Islands on August 6. The very warm waters of the northwestern Caribbean Sea allowed the storm to begin another phase of rapid intensification. Allen reached its second and greatest peak intensity on the afternoon of August 7, with maximum sustained winds of 190 mph (305 km/h) and a minimum barometric pressure of 899 mbar (26.5 inHg). Allen had the highest maximum sustained winds ever recorded in an Atlantic hurricane. Its minimum pressure of 899 millibars was the second-lowest pressure on record for the basin at the time. The major hurricane was also very large at this time, with hurricane-force winds extending 144 mi (232 km) from its center and tropical-storm-force winds extending 345 miles. Allen's circulation filled nearly the entire Gulf of Mexico, and was regarded at the time as the second-largest Atlantic hurricane on record, after 1961's Hurricane Carla. Continuing westward, the southern portion of Allen's circulation passed over the Yucatán Peninsula, causing the cyclone to weaken again. Allen bottomed out with winds of 130 mph (210 km/h) on August 8. Continued movement west over the warm waters of the Gulf of Mexico allowed Allen to restrengthen into a Category 5 hurricane for a third time as it moved over the open waters of the Gulf. The hurricane's central pressure dropped back to a tertiary low of 909 mbar (909 hPa; 26.8 inHg). Pressure falls over the southern United States at this time indicated Allen would soon slow its forward motion as it approached Texas. Allen's forward speed slowed considerably in the hours before it made landfall near Brownsville as a low-end Category 3 major hurricane on August 10. The storm rapidly weakened as it moved inland, eventually dissipating over the mountainous terrain of northern Mexico the following day.

As Allen approached the Caribbean Sea, gale warnings and a hurricane watch were issued for the islands of Barbados, St. Lucia, St. Vincent, Dominica, Grenada, Martinique, and Guadeloupe during the daylight hours of August 3. Gale warnings were in effect for Antigua from 11 am on August 3 until 11 am on August 4. Hurricane warnings were raised for Barbados, St. Vincent, St. Lucia, Martinique, and Dominica from the early afternoon of August 3 until the late morning of August 4. As Allen moved into the Caribbean sea, hurricane watches were issued for southeastern sections of the Dominican Republic and the southwestern peninsula of Haiti from 11 am on August 4 until the morning of August 5. Gale warnings were then in effect for the southern Dominican Republic from the night of August 4 into the night of August 5, while southern Haiti maintained the warnings from the night of August 4 into the morning of August 5. The hurricane watch was issued for Jamaica during the morning hours of August 5, while hurricane warnings were raised for the southwest peninsula of Haiti from the late morning of August 5 into the morning of August 6. Hurricane warnings went into effect for Jamaica from around noon on August 5 until late in the afternoon of August 6. The Cayman Islands saw hurricane watches issued from the afternoon of August 5 into the morning of August 6 before the watches were upgraded to hurricane warnings from the morning until late afternoon of August 6.

As Allen approached the Gulf of Mexico, hurricane warnings were raised for the northeast Yucatán peninsula of Mexico from the afternoon of August 6 into the morning of August 8. Gale warnings were in effect for the Florida Keys from the evening of August 6 into the early morning of August 8. As Allen approached its final landfall, the northeast Mexican coast and Texas coast were placed under a hurricane watch from the morning of August 8 until the morning of August 9 for Mexico and the afternoon of August 9 for Texas. Hurricane warnings were posted for the Texas coast during the afternoon of August 8, and were lowered north of Freeport, Texas during the afternoon of August 9 and south of Freeport during the afternoon of August 10. Gale warnings and a hurricane watch were issued for the Louisiana coast from Vermilion Bay westward from the afternoon of August 8 into the afternoon of August 9. Hurricane warnings were in effect for northeast Mexico from the early afternoon of August 9 into the late afternoon of August 10. Hurricane warnings were downgraded to gale warnings between High Island, Texas and Freeport, Texas between the late afternoon of August 9 and the late afternoon of August 10. Hurricane watches were dropped for the Louisiana coast during the late afternoon of August 9. Hurricane warnings were downgraded to gale warnings for the lower Texas coast south of Freeport from the late afternoon of August 10 into the early morning of August 11.

In addition to the various watches and warnings put in place ahead of Allen's arrival, various international governments took measures to prepare for the hurricane in Haiti. A disaster committee and executive committee to address the aftermath of the storm was formed by Haitian President Jean-Claude Duvalier, the latter of which was headed by members of the Haitian Ministry of Health and Hatian Red Cross, while members of the committees included representatives from the army, Pan American Health Organization (PAHO), United States Agency for International Development (USAID), and others. Emergency instructions were issued by the Haitian government to prevent possible increases in malaria cases following Allen's passage. The United States government made preparations to send personnel, as well as financial and aerial assistance, to Haiti. In neighboring Cuba, over 200,000 people across seven provinces were evacuated.