Hurricane John (1994) - Meteorological History

Meteorological History

The United States' National Hurricane Center (NHC) later identified the precursor to Hurricane John as a tropical wave that moved off the coast of Africa on July 25, 1994. The environment in the Atlantic Ocean was hostile to tropical development, so the wave continued without developing until reaching the Eastern Pacific on August 8. It slowly organized, and on August 11 was recognized as Tropical Depression Ten-E 300 nautical miles (560 km) south-southeast of Acapulco, Mexico. Conditions were not ideal for development, but it quickly developed banding features and well-defined outflow, and was upgraded to a tropical storm and named Tropical Storm John later that day.

A strong ridge of high pressure over the Northeastern Pacific Ocean forced John westward, where upper level wind shear kept John a tropical storm. Intensity fluctuated considerably, however, as shear levels varied. More than once, shear cleared away most of the clouds above John and nearly caused it to weaken to a tropical depression. However, after eight days of slow westward movement across the Pacific Ocean, shear lessened greatly on August 19, and John intensified significantly and was designated as a hurricane at 1700 PDT. During an eighteen-hour period between August 19 and August 20, John further strengthened from a weak Category 1 hurricane to a major Category 3 hurricane. Around 1100 PDT on August 20, it crossed into the central Pacific, the first of three basin crosses John would make.

After entering the central Pacific, John left the area monitored by the NHC and was instead monitored by the Central Pacific Hurricane Center (CPHC). As it moved slowly westward, Hurricane John continued to strengthen considerably in an increasingly favorable environment well south of the Hawaiian Islands; on 22 August John was designated a Category 5 hurricane on the Saffir-Simpson Hurricane Scale (the highest classification for hurricanes) and later that day (by Hawaii Standard Time) reached its peak winds of 175 miles per hour (280 km/h). Also on August 22 (by Hawaii Standard Time), John made its closest approach to the Hawaiian Islands, 345 miles (500 km) to the south. John had threatened to turn north and affect the islands days before, but the ridge of high pressure that typically shields the islands from hurricanes kept John on its southerly path. Nonetheless, heavy rains and wind from the outer bands of John affected the islands.

With the Hawaiian islands behind it, John began a slow turn to the north, taking near-direct aim at Johnston Atoll, a small group of islands populated only by a United States military base. The storm slowly weakened from its peak as a Category 5 hurricane in the face of increasing shear, dropping down to a Category 1 hurricane with 90 miles per hour (145 km/h) maximum winds. On August 25 local time, John made its closest approach to the Johnston Atoll only 15 miles (24 km) to the north. On Johnston Atoll, sustained winds were reported up to 60 miles per hour (95 km/h), the equivalent of a strong tropical storm, and gusts up to 75 miles per hour (120 km/h) were recorded.

Clearing Johnston Atoll, John turned to the northwest and began strengthening again as shear decreased. On August 27 local time, John reached a secondary peak strength of 135 miles per hour (210 km/h), and shortly thereafter it crossed the International Date Line at approximately 22° N and came under the surveillance of the Guam branch of the Joint Typhoon Warning Center (JTWC). By crossing into the western Pacific, John also became a typhoon and was referred to as Typhoon John during its time in the western Pacific. Immediately after crossing the Date Line, John again weakened and its forward motion stalled. By September 1, John had weakened to a tropical storm and was nearly motionless just west of the Date Line. There, John lingered for six days while performing a multi-day counterclockwise loop. On September 7, a trough moved into the area and quickly moved John to the northeast. John crossed the Date Line again on September 8 and reentered the central Pacific.

After reentering the central Pacific, John briefly reached a tertiary peak strength of 90 miles per hour (145 km/h), a strong Category 1 hurricane, well to the north of Midway Island. However, the trough was rapidly pulling apart John's structure, and the cold waters of the northern central Pacific were not conducive to a tropical cyclone. On September 10, the 120th advisory was released on the system, finally declaring John to have become extratropical approximately 1000 miles (1600 km) south of Unalaska Island.