Category 5. Only the most powerful of the most powerful storms on Earth reach this ominous peak. It’s a designation that occurs when hurricanes achieve a highly destructive wind strength greater than 156 mph. Usually relegated to late season storms that form and strengthen when the ocean surface temperature is at its hottest, it is a very, very, very rare event to see any storm approach Cat 5 status at the start of hurricane season.
Water temperatures are typically not high enough to support such a monster event so early.
But this Sunday, just six months after the Western Pacific spawned Typhoon Haiyan, the most powerful storm ever to strike the land, the three-day-old hurricane Amanda raged to just shy of Cat 5 status in the Eastern Pacific. Peaking at a maximum sustained wind speed of 155 mph, the storm teetered at the edge of highest intensity category even as it roared its way into the record books as the mightiest storm ever recorded for this region of the world in May.
(Hurricane Amanda at strong Category 4 status on May 25. Image source: LANCE-MODIS.)
By comparison, the storm Amanda beat out, Adolph, was also a rather recent event, forming on May 25 of 20o1 and reaching a peak intensity of 145 mph on May 29th.
Hot, Deep Water
Hurricane season in the Eastern Pacific starts on May 15. Amanda began to gather just four days after, as a tropical disturbance, on May 19th. The storm gradually gained strength as it drifted north and west into extraordinarily warm waters that ranged from 1 to 3.6 C above typical temperatures for this time of year. By Sunday, May 25, the storm had exploded to just shy of category five status.
Extreme heat intensity fueling Amanda came from a Pacific Ocean exploding with warmth. The equatorial Pacific was just tipping into the hot ocean surface event that is El Nino even as overall Pacific anomalies ranged near 0.8 C above the, already hotter than normal, 1979 to 2000 average. The net result was that Amanda was fueled by sea surface temperatures in the range of 27 to 30 degrees Celsuis with hurricane-supporting warmth pushing as far as 50 meters into the depths. As a result, cool ocean water upwelling through Ekman pumping had far less effect on this storm than is typical for early in the season when the sun’s rays usually have not pushed warmth so deep.
(Today’s ocean surface temperature anomaly at +1.13 C on May 28th. Global Ocean surface temperature anomalies have been in the record range of +1 C above 1979-2000 values all throughout May. Hot ocean surface temperatures of this kind is hyperfuel for hurricanes. It is no accident that the record storm that was Amanda formed in the visible hot pool off the west coast of Mexico. Image source: University of Maine.)
Hurricanes are nothing if not ocean heat and moisture engines. The storms feed on hot air rising off the ocean surface, and their cyclonic action churns the waters below them eventually limiting their intensity as the strongest storms dredge into cooler waters. But with human warming, both the ocean surface as well as the waters far below show ever increasing heat potentials. This heat is nothing if not high-efficiency energy for oceanic, warm core cyclones.
Global Warming Heat Engine — Lengthens Storm Season, Generates More Powerful Cyclones
Amanda’s anomalous intensity was, thus, no accident. Instead, it was directly related to the extreme ocean heating that is an attribute of human-caused warming. The danger here is not only for more intense storms and for more intense storms coming earlier and earlier in the year, it is also for a general lengthening of the period during which these powerful storms emerge. The risk, therefore, is that hurricane season will extend deeper into the Spring and further into Fall for both the Eastern Pacific and the Atlantic. And during this ever-growing storm year the higher heat values increase the likelihood of monster storms reaching and exceeding category five strength.
The currently explosive Western Pacific may well foreshadow events for other regions of the world. That volatile storm zone already sees some seasons featuring year-round hurricanes and tropical storms. And the already intense cycle there is also likely to strengthen as the oceans continue to warm.