Hurricane Agatha caught my attention the other day. Eastern Pacific hurricanes tend to do that. Eastern Pacific hurricanes that make landfall moreso. Eastern Pacific hurricanes that make landfall in May even moreso. Eastern Pacific hurricanes that do so in May during an ENSO La Niña year? ??…
Agatha came ashore on May 30 in the Mexican state of Oaxaca. It did so as a CAT 2 storm with sustained wind speeds of 105 mph. The strongest hurricane to make landfall on Mexico’s Pacific Coast, it’s only the third (since records have been kept) to do so in May (the other two are the same-named hurricane of May, 1971, and Barbara of May, 2013).
Why is this so unusual?
First: Even with high sea surface temperatures (SST, more below on that…), the prevailing NE Trade Winds tend to push developing systems to the west into the open central Pacific before they can become organized as actual hurricanes. Second: The opportunity for a developed system to “back-up” against the prevailing winds and actually approach the Pacific coast from the S-SW is extremely rare, requiring some unusual atmospheric conditions. Third: The formation of a hurricane in the eastern Pacific is more likely to occur later in the summer (August to September) as SST (if they get there at all) pass the 80ºF threshold. Finally: This happened in an ENSO (El Niño – Southern Oscillation) year when all the oceanic – atmospheric parameters indicate a third straight year of La Niña conditions in the eastern Pacific.
La Niña conditions are not conducive to hurricane formation in the eastern Pacific (El Niño conditions are). During a La Niña year ocean surface temperatures are depressed relative to “normal”and “El Niño” years. The atmosphere, especially in the context of wind shear, is more likely to destabilize developing systems, not allowing them to get organized. In the case of Hurricane Agatha, the SST in the Gulf of Tehuantepec was a robust 86ºF, well above the 80º threshold necessary. Additionally, an unusual and strong low pressure trough was located to the NE, drawing the organizing hurricane in that direction, overcoming the prevailing trade winds. Why such a high SST in May, especially given the overall lower-than-normal SST for the eastern Pacific up to that point? I’m not sure. I’ll keep watching…
Hawaii is some 65º of longitude and 4100 miles west of the Gulf of Tehuantepec. Critically, although still in the tropics, the islands are 8º latitude farther north, and at 22º N latitude, nearly out of the tropics (which extend from 23.5ºS to 23.5ºN). This “edge” position in the tropics becomes important in the next part of the story…
Hawaii experiences hurricanes. However, hurricanes in the islands are not frequent; there is not a summer/fall hurricane season similar to that experienced by such places as Japan, Taiwan and the Philippines in the western Pacific (where hurricanes are referred to as typhoons). The “edge” position of the islands places them against a mid-latitude high pressure system to the north that is often referred to – with a certain sense of humor, I think – as the “Hawaiian High”. As a result of this close juxtaposition, developing/developed hurricane systems coming across the equatorial Pacific from the east often pass to the south of the islands. However, if the Hawaiian High should destabilize or shift slightly (to the east), hurricanes can bend around the corner of the high pressure ridge, and run NW to N across the islands. Which takes us to the next part of the story…
On September 11, 1992, Hurricane Iniki came around the corner…ran north and right over the island of Kauai. A monster CAT 4 storm, it had sustained winds of 145 mph, with numerous gusts over 200 mph. The south coast of the island took the brunt of a storm surge with waves up to 20′. The fortunate part is that the quick passage over the island (it took a grand total of 40 minutes) left little time for massive rainfall to further batter the island. Spawned in the middle of the 1990-1995 El Niño cycle, the fast-moving storm lasted another two days before dying out…halfway across the north Pacific to Alaska.
$3.1 billion later (1992 USD), Kauai’s communities and services (electrical and phone services were especially hard hit) were restored. However, with respect to a certain segment of island housing, replacement came too late…
Chickens… Feral chickens… It’s supposed to be a pleasant picnic lunch here in upper Waimea Canyon. It’s 1992 all over again, except this time as Under Siege. The beady-eyed leader of the foul fowl flock in fact reminds me a little of Tommy Lee Jones (don’t get me wrong, I’m a big fan…). We beat a hasty retreat to the car, our lunch and ourselves mostly intact…
Gallus gallus: the Red Jungle Fowl of central, southeast and oceanic Asia. G. is the ancestor of modern chickens (Gallus domesticus) and has been with us at least since the end of the Pleistocene (10,000 years). SE Asian peoples started the domestication process about 8000 years ago; Polynesians got into the act about 5000 years ago, and brought them to the Islands sometime between 500-700 AD. Why are they so numerous on Kauai? Prior to 1883 they were on all the islands. It was at that time that the sugar cane farmers on the other islands introduced the mongoose to combat rats in their fields (another interesting Hawaii story). It was a spectacular fail with respect to the rats, but a stunning success with respect to (mostly) flightless fowl.
Stopped on the road, waiting for another flock to cross, I’m reminded of the local’s “chicken crossing the road” joke: “Why did the chickens cross the road?…because they own it…and everything else on Kauai”.
Author’s Note: In 1982 Hurricane Iwa passed within about 25 miles of the island and also did considerable damage, including to chicken coops. So in some respects the outbreak was on even earlier. However, the “Great Escape” was that in 1992; Steve McQueen would have been proud.
