page_title: Cyclone Alan
section_title: Meteorological history
hierarchical_section_title: Cyclone Alan / Meteorological history
caption_attribution_description: English: Track map of Tropical Storm Alan of the 1997-98 South Pacific cyclone season. The points show the location of the storm at 6-hour intervals. The colour represents the storm's maximum sustained wind speeds as classified in the Saffir-Simpson Hurricane Scale (see below), and the shape of the data points represent the nature of the storm, according to the legend below. Saffir-Simpson Hurricane Scale Tropical depression&lt;39 mph&lt;63 km/h Category 3111–129 mph178–208 km/h Tropical storm39–73 mph63–117 km/h Category 4130–156 mph209–251 km/h Category 174–95 mph119–153 km/h Category 5&gt;156 mph&gt;251 km/h Category 296–110 mph154–177 km/h Unknown Storm typeTropical cycloneSubtropical cycloneExtratropical cyclone / Remnant low / Tropical disturbance
context_page_description: Tropical Cyclone Alan was considered to be one of the worst natural disasters experienced in French Polynesia. The system, first noted as a tropical disturbance on April 17, 1998 east of the Northern Cook Islands, initially moved erratically prior to its designation as Alan upon developing into a tropical cyclone on April 21. The following day, Alan reached its estimated peak intensity with 10-minute maximum sustained wind speeds of 75 km/h, posing several forecasting challenges due to difficulties in establishing its location and intensity. On April 23, Alan appeared to become sheared with the low-level circulation center displaced about 20 km from the nearest atmospheric convection. However, over the next day, after the mid-level trough of low pressure shearing the system moved faster than expected, Alan became better organized. While situated about 555 km west-northwest of the French Polynesian island of Tahiti, the system drifted south-southeastward. Early on April 25, Alan passed near to or over the French Polynesian Society Islands of Maupiti, Bora-Bora, and Raiatea.
context_section_description: On April 17, 1998, the Fiji Meteorological Service (FMS) started to monitor the development of a tropical disturbance east of the Northern Cook Islands. Before the FMS initiated advisories on the system on April 19, the system moved erratically; it later developed into a weak depression while it located about 555 km (345 mi) north of Manihiki Atoll in the Northern Cook Islands. Over the next couple of days, the system slowly moved northwards, gradually organizing, with gale-force winds developing in its southern quadrant on April 20. Over the next day, the system developed into a category 1 tropical cyclone on the Australian tropical cyclone intensity scale, and the FMS subsequently named the system Alan at 1800 UTC. By this time, the cyclone, located about 300 km (185 mi) east-southeast of Manihiki, started to move westwards. On April 22, the FMS estimated that Alan reached its peak intensity with 10-minute maximum sustained wind speeds of 75 km/h (45 mph), just as the system started to pose several forecasting challenges due to difficulties in establishing its location and intensity. Later that day the Naval Pacific Meteorology and Oceanography Center (NPMOC) started to issue warnings on Alan and accidentally assigned it the designation 32P as opposed to 36P, estimating peak 1-minute sustained wind speeds of 85 km/h (50 mph).
  On April 23, the system appeared to become sheared, with the low-level circulation center displaced about 20 km (10 mi) from the nearest atmospheric convection. As a result, the FMS reported Alan's weakening into a depression, while the NPMOC subsequently issued their final advisory on the system. Over the next day, as a mid-level trough of low pressure shearing Alan moved faster than expected, the depression became better organized and developed favorable upper-level outflow. As a result, the NPMOC initiated advisories on the system again on April 24, and later that day, the FMS reported that Alan re-intensified into a Category 1 tropical cyclone. While located about 555 km (345 mi) west-northwest of the French Polynesian island of Tahiti, the system moved south-southeastward under the influence of an upper-level anticyclone located to its east. Early on April 25, Alan passed near to or over the French Polynesian Society Islands of Maupiti, Bora-Bora, and Ra'iātea. As the system moved near Bora Bora, a maximum wind gust of 147 km/h (91 mph) and a pressure observation of 1002 hPa (29.6 inHg) were recorded, indicating the minimal strength of Alan; however, the wind gust was stronger than that expected of similarly intense tropical cyclones. It was later speculated that squalls within Alan's convective feeder band may have been responsible for the stronger wind gusts. On April 25, strong wind shear pulled the system apart, with visible imagery revealing a fully exposed low-level circulation. As a result, the FMS reported that the system weakened into a depression at 1800 UTC that day, while located about 185 km (115 mi) west-northwest of Tahiti. The NPMOC subsequently reissued their final advisory early the next day as the system drifted south-southeastward while located west of Tahiti.
caption: Map plotting the track and the intensity of the storm, according to the Saffir–Simpson scale
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