Hurricane Juliette (2001) - Meteorological History

Meteorological History

The tropical wave that later produced Juliette first produced Tropical Depression Nine in the Atlantic Ocean. Forming in the Caribbean Sea, the depression dissipated over Central America on September 20, a day after formation. By early on September 21, the remnants of Nine had re-organized in Pacific, and was then upgraded into a tropical depression. Six hours later, the depression was upgraded into a tropical storm. However, the storm was not named Juliette until later that day, when the storm was operationally believed to have formed (which came after reports from a Hurricane Hunter aircraft).

In an environment of light wind shear, meteorologists predicted to new system to reach hurricane intensity within two days. Within 100 mi (160 km) off the coast of Guatemala, the system moved generally west-northwest over the next five days, paralleling the Mexican Riviera. While a major decrease in thunderstorm activity initially inhibited intensification it became better organized on September 22. By the afternoon of september 23, Juliette had became a hurricane, with maximum sustained winds reaching 75 mph (120 km/h).

Upon becoming a hurricane, infrared imagery suggested that the hurricane had developed a pinhole eye. Forecasters were also expecting Juliette to reach major hurricane status, Category 3 or higher on the Saffir-Simpson Hurricane Scale. Steadily moving west, the storm underwent rapid deepening. By 1800 UTC September 23, Juliette had reached Category 2 status, with winds of 100 mph (145 km/h). Shortly thereafter, the hurricane intensified into a Category 4 storm; bypassing the Category 3 stage, an unusual occurrence for a tropical cyclone. In all, Juliette had intensified 60 mph (130 km/h) in 18 hours.

After reaching its secondary peak as a low-end Category 4 hurricane, microwave and Hurricane Hunter data indicated that Juliette underwent an eyewall replacement cycle. Subsequently, Juliette weakened into a Category 3 hurricane on September 24, and then into a high-end Category 2 system, with 110 mph (160 km/h) winds. However, by September 25, Juliette had completed the cycle, and quickly regained major hurricane status. The hurricane developed very cloud top temperatures. along with a classic structure of an intense hurricane and a very well-defined eye. A large hurricane, Juliette reached its peak intensity of 145 mph (230 km/h) the same day. Around that time, Reconnaissance Aircraft reported a minimum central pressure of 923 mbar, the third lowest measured pressure ever recorded in the basin behind Hurricane Ava in 1973; other hurricanes such as Hurricane Linda during 1997 have had lower pressures estimated via satellite imagery.

Shortly after its peak, a strong trough of low pressure brought Hurricane Juliette northward, where the cyclone moved over cooler water temperatures. While Juliette initially maintained well-defined banding features and an impressive upper-level outflow, and another eyewall replacement cycle took toll on the storm, this time three centric eyewall formed compared to the normal two, a very rare occurrence. Moving much further east than anticipated, an eye was no longer visible on satellite imagery by September 27.

Juliette slowed its forward motion as it continued north-northwestward, and weakened to a tropical storm on September 28. Even though thunderstorm activity decreased markedly, Tropical Storm Juliette maintained a well-defined atmospheric circulation and a large area of gale-force winds. A small area of warm waters near the Baja California Peninsula allowed the storm to re-strengthen into a hurricane early on September 29 as convection increased. At this time, computer models suggested two distinct possibilities of the storm's path. Some suggested Hurricane Juliette to move inland while others expected the hurricane to parallel the peninsula.

Meandering offshore, the center soon became difficult to locate. The low-level circulation became exposed from the deep convection as increased vertical shear again took toll Juliette, and the storm hit Baja California near Cabo San Lucas as a minimal tropical storm at 0000 UTC September 30. Although scientist noted the possibility of slight re-intensification over the Gulf of California, Juliette's low level circulation remained as it crossed the peninsula, and it restrengthened in the northern Sea of Cortez as the circulation became better defined. Lacking deep convection, it drifted westward, where, after making a landfall northeastern Baja California, it finally dissipated early on October 3.