Tremendous Rainfall over Chuuk from TS Chata'an

This page documents some aspects of the impacts of Tropical Storm Chata'an as it formed near Chuuk in June/July of 2002. Chuuk is a group of islands in the Federated States of Micronesia. 

Given the extreme rains and subsequent landslides that occurred as TS Chata'an passed over Chuuk, it is interesting to consider whether the topography enhanced the rainfall.  The rainfall tally (see the 'event summary page').  It is likely that the orography had little to do with the tremendous totals observed at the Truk International Airport (PTKK), especially considering the prevailing wind direction during the event. The rainfall that occurred over the higher peaks could have been enhanced, however. Whether or not the rainfall was enhanced at higher elevations is not very important, because the rainfall observed at the airport was clearly enough to cause catastrophic landslides.   

The high terrain on Tol and Moen reaches 1453 feet and 1224 feet respectively, which is sometimes above the cloud condensation layer. The peaks are relatively isolated, but perhaps can 'trigger' downstream showers and thunderstorms. It is likely that feeder/seeder and other orographic processes enhance rainfall over the high terrain as exemplified by the annual rainfall totals of 400+" at Kauai. Granted, these islands are smaller (2-6 miles in length/width) and shorter than Kauai (~35 miles in diameter, peak at 5170 feet), so they don't have scale working on their side, but I would expect some (at least a little, maybe 5-10% ?) orographic enhancement of rainfall totals. It would be an interesting question to investigate with some high resolution boundary layer/microphysics modeling. 

On the subject of heavy rainfall, it's worth pointing out the notable totals measured on nearby islands during the formative stages of Chataan.

Nukuoro which measured 20.16" from 11Z June 27 to 13Z June 29 (I was gone over the weekend and missed the observations that occurred later). The highest sustained wind during that time period was 39 kts (08Z June 29) with a gust to 55 kts (06Z June 29).

Satawan reported 13.72" during the same time period.

Oroluk, which apparently doesn't report rainfall, measured sustained winds of 37 kts with a gust to 49 kts at 13Z July 1.  

Click on the thumbnail for a location map for these reporting stations. [20 Kb].  [Source: NWSFO Tiyan, Guam]

I've assembled the METARs for the event as well as a summary table giving the 6 and 24-hr rainfall totals. Find it here:

In the days before formation, Chuuk received typical rainfalls in keeping with climatological normals. Significant rain fell during the formation stage, while Chata'an was quasi-stationary. As the storm organized, it actually moved away from Chuuk, then turned back and passed over Chuuk on the third, dropping torrential rainfall, with 19.86" falling in 18 hrs, and 7.83" in 6 hrs.

rainfall prior to formation (June 16-22):    2.63"

rainfall during formation (June 23-30):     12.48"

rainfall during passage (July 1-3):            24.50"    Peak wind: 44 kts from 190º at 0529Z on July 3

rainfall after passage (July 4-5):               0.59"

Given the generally mountainous/hilly terrain of the inner lagoon islands, significant flooding and numerous landslides occurred. Fatalities were reported in most villages on Weno (Moen), which is the commercial center of Chuuk State, population 17,000. A total of about 50,000 people live on the islands in Chuuk Lagoon, with another 15,000 living on outer islands in Chuuk State (mostly to the north and west).

To put this event in historical climate terms, I pulled off the following graphs (click the thumbnail to view) off of the NCDC web page. Apparently, in the past 8 years, the highest observed wind gust was 46 kts and the greatest 24-hr rainfall was about 6". For more info on the Chuuk's climate history, click the following link:

To summarize, this event is a good example of how forming/intensifying systems can have deadly impacts is often the heavy rainfall produced in the deep convection.  Tragically, the heavy rainfall has triggered massive landslides on most of the inner islands of Chuuk Lagoon. Preliminary reports indicate that at least 39 have died and about 1500 homes were destroyed.  For archived media reports on this disaster, click the following link:

This is a sobering reminder of the vulnerabilities of many island nations, not just to strong typhoons, but also the other effects of even weak tropical cyclones.

Jonathan Vigh

Graduate Research Assistant, Colorado State University

Posted: July 3, 2002, updated July 8, 2002 and April 25, 2004.