(Iselle [center frame] and Julio [right frame] take aim on Hawaii [upper left] in most recent LANCE MODIS satellite shot.)
The Northern Pacific has been a very hot place this year. Above the Equator and stretching from Asia to the West Coast of North America, very few regions have witnessed below normal temperatures. And numerous very large hot zones continue to dominate off of Central and North America, between Alaska and Russia, and near Japan.
Overall, Pacific Ocean temperatures today are an excessive +0.93 degrees C above the, already hotter than normal, 1979 to 2000 average. And this extra heat, fueled by global warming, provides energy for the propagation of tropical cyclones well outside of their traditional ranges.
For Hawaii, this means falling under threat of two cyclone strikes within the period of as many days.
Hot Pacific Waters Projected to Spawn More Hawaiian Storms
Cyclone strikes in Hawaii are rare. The last time the island state was pummeled by a tropical storm was during the 1992 El Nino. But now it is threatened by not one, but two hurricanes. It is an event that is unprecedented in the entire satellite record. In other words, we’ve never seen this before.
(Global sea surface temperature anomaly on August 6, 2014, shows an extreme +1.11 C positive temperature departure for the globe and a very strong +0.93 positive temperature departure for the North Pacific. Current science shows that warming ocean waters are extending the northward ranges of tropical cyclones, bringing regions like Hawaii under increasing threat. Image source: University of Maine.)
A shift in hurricanes toward Hawaii wasn’t entirely unexpected, however.
In 2013, Hiroyuki Murakami, from the International Pacific Research Center at the University of Hawaii at Mano together with a team of ocean and atmospheric researchers produced a report for Nature entitled Projected Increases in Cyclones Near Hawaii. The study modeled expected increases in Pacific Ocean surface temperature driven by human-caused climate change in the region near Hawaii. What it discovered was a marked increase in storm formation near Hawaii due to warming waters and related atmospheric changes.
The paper notes:
A key factor in projecting climate change is to derive robust signals of future changes in tropical cyclone activity across different model physical schemes and different future patterns in sea surface temperature. A suite of future warming experiments (2075–2099), using a state-of-the-art high-resolution global climate model1, 2, 3, robustly predicts an increase in tropical cyclone frequency of occurrence around the Hawaiian Islands.
(Change in tropical cyclone frequency between now and 2075-2090 according to model projections produced in the Murakami Paper. Image source: Nature. See Also: Climate Change May Increase Number of Hawaiian Hurricanes)
What these researchers might not have expected was that a very warm Pacific during 2014 might well provide a prelude to what their models were predicting.
Iselle and Julio Barreling On In
For forecasts now show that Hawaii may well be in for a dose of double trouble — an extended period of stormy conditions starting early Friday and possibly not letting up until Monday as the unheard of storm pair barrels on in.
As of the most recent advisory, 85 mph hurricane Iselle was located about 650 miles to the east and southeast of Hilo. Iselle’s present and projected motion toward the west and northwest at around 15 miles per hour is expected to bring the storm, at a strong tropical storm intensity, over Hawaii’s Big Island by Friday. The storm is then projected to pass near the eastern islands before tracking back out into the open Pacific.
Coming directly behind Iselle, Julio is located about 1600 miles east-southeast of Hilo and packs maximum sustained winds of 75 miles per hour. The storm is also expected to weaken to strong to moderate tropical storm status before passing over or near the Hawaiian Island Chain along a track just to the north of Iselle’s path. This would bring the storm near the islands on Sunday, just two days after Iselle.
(Threat cones for Iselle, Julio and Genevieve, all developing in an unusual region near the Central Pacific. Image source: NOAA.)
It’s worth mentioning that a third storm, Genevieve, has also developed in the mid-Pacific within about 1,000 miles of the Hawaiian chain — also in a rather rare region for tropical cyclone formation. Genevieve, however, is not expected to threaten the islands as it tracks westward, taking a long journey toward Asia.
Conditions in Context
These three cyclones generated over warm waters near the central equatorial Pacific. The storms emerged from a convective pattern in a region that typically only shows robust storm development during El Nino.
Though El Nino is not officially ongoing, atmospheric conditions over the past few weeks have become more favorable even as a new warm Kelvin Wave appears to be forming in the waters of the Western Pacific. NOAA still forecasts a weak to moderate El Nino for 2014, but conditions, though somewhat more favorable, remain murky.
(Current sea surface temperatures in the region of Hawaii are a in rather warm and mostly above average range from 26 to 28 C [80 to 83 F], more than enough to sustain powerful tropical cyclones. Generally, water temperatures above 75 F are needed for tropical cyclone formation and strengthening. The primary limiters to both Eselle’s and Julio’s strength remains wind shear, which is expected to reduce both storms to tropical storm status over the coming days. Even so, Hawaii is in for an ongoing period of unprecedented weather. Image source: National Hurricane Center.)
It’s worth noting that a rash of storms in this region is unprecedented in the satellite era and is especially odd considering that ENSO remains neutral. It is very likely that the outbreak is in some way related to the larger Pacific Ocean warming trend associated with human-caused climate change acting together with an El Nino-like development trend.
UPDATE: Due to warm surface waters in the region of Hawaii and somewhat more favorable than expected atmospheric conditions, Iselle is expected to make landfall on the big island of Hawai’i near Hawaii City later today. Expected maximum sustained winds at the time of landfall are near 75 miles per hour.
Hurricane tracking from NOAA brings the storm directly over the Big Island at around midnight after which the storm is predicted to skirt Maui and Oahu:
(NOAA’s most recent projected storm track for Iselle. Image source: National Hurricane Center.)
Hat tip to Eleggua