Tropical Storm "Dolphin" Near Pohnpei, Micronesia!

Saturday, May 9, 2015
11:46 pm

Me in a mangrove forest as part of a UW study abroad trip in Pohnpei, Micronesia during the summer of 2013.

Almost two years ago, I went on a UW study abroad trip to Pohnpei in the Federated States of Micronesia to learn about coastal ecosystems, and it was truly life-changing, in more ways than one. I had an amazing time while I was there, but I actually had seizures (I have epilepsy) and was ordered to leave prematurely by the UW. My mom got a free plane ride over as part of our travel insurance, and we traveled back, but not before spending over a week in Kona, Hawaii, and having amazing experiences there. We had really shoddy internet access while we were in Pohnpei, but I was still able to thoroughly document my experiences via blogs. If you look through the June/July blogs from 2013 (see the archive on the left), you’ll see all my Micronesia and Hawaii posts. These are my favorite posts I’ve ever made – by a long shot.

Before I start, let me just clear up one misconception: “Micronesia” and the “Federated States of Micronesia (FSM)” are not the same. Micronesia is a geographic region encompassing tens of thousands of islands and 6 sovereign nations. Guam is in Micronesia. The Federated States of Micronesia are a group of four island states; from west to east (and, coincidentally, north to south), they are they are Yap, Chuuk, Pohnpei, and Kosrae. The coordinates range from 9.5° N, 138° E (Yap) to 5.3° N, 163.0° E (Kosrae). Pohnpei is around 6.8° N, 158° E.

One thing we talked about as soon as we got there was that Pohnpei rarely experienced hurricanes. The reason was its proximity to the equator. The Coriolis force, which causes everything from moving parcels of air to Felix Hernandez’ devastating changeup to deflect to the right in the Northern Hemisphere and left in the Southern Hemisphere, is at a maximum at the poles and a minimum (zero) at the equator, so when you are within 5 degrees of the equator, air tends to not rotate around a storm, which is what you need for cyclogenesis.

One map that really shows this is a simple map of all the cyclones tracks from 1985-2005 over all ocean basins. You can clearly see that there are no cyclones forming within approximately 5 degrees of the equator. The black star I put on the map is the approximate location of Pohnpei. Notice how it is just on the edge of the area where cyclones start to form there, and that the cyclones that do impact it are generally pretty weak (stronger ones are in orange and red, weaker ones are in blue).

Data from the Joint Typhoon Warning Center and the NOAA. Retrieved from Wiki Commons

The above picture also clearly shows the 7 cyclone ‘basins’ – the North Atlantic, the Northeast Pacific, the Northwest Pacific, the Southwest Pacific, the Southwestern Indian, the Southeastern Indian, and the Northern Indian. The Northwest Pacific is by far the most active basin, averaging 26 cyclones a year. The North Atlantic Basin only averages 11.

The seven cyclone basins. Credit: NOAA

Let’s take a look at what the satellite over Pohnpei looks like right now. This is the most recent visible satellite from the Aqua polar orbiter satellite, taken around 7 P.M. Sunday FSM time. Pohnpei is that small island in the middle.

Retrieved from NASA’s Worldview Satellite Page

You can see there is a tropical storm – Tropical Storm Dolphin – that is really bearing down on Pohnpei. Thankfully, the maximum sustained winds are currently around 40 mph, barely tropical-storm-force. However, I wouldn’t be as concerned about the winds or waves as I would be about the rain. Pohnpei is a very mountainous island, and heavy rains over the mountains could result in the inundation of piggeries in rural areas or flash flooding in cities that are within close proximity to rivers. Pohnpei is one of the wettest places on earth… the rainfall ranges from 140 inches per year near the airport to over 325 inches per year over the mountains. When I was there, I experienced some of this rainfall first-hand.

In fact, here’s a little video I took of a rainstorm as it passed by while I was at our hotel on the Soundau Estuary.

Why does Pohnpei get extraordinary rainfall rates? It’s because they get incredibly tall thunderstorms due to tons of heat energy and a very high tropopause. When a 70,000 foot cloud passes over you, you are going to get dumped on.

One more video… not only to show you how stunningly beautiful Pohnpei is, but how mountainous it is. Many islands in the Pacific are in danger of becoming completely submerged due to rising sea levels over the next century. Pohnpei is not one of them. These mountains significantly amplify precipitation not only due to orographic effects but due to upslope flow converging over the mountain peaks and causing convection over the mountains to cause those 70,000 foot thunderheads.

Meanwhile… we might get a few hundredths of an inch of rain on Monday. If you live between Olympia and Portland though, be on the lookout for some heavy rain Monday night and Tuesday night.

Enjoy the rest of your weekend!
Charlie

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