Tropical storms – cyclones, hurricanes, typhoons – are elaborate mechanisms by which heat energy is transferred from the tropics to the northern latitudes. Puerto Rico is under threat from hurricanes each season. In fact, the word hurricane is derived from ‘huracan’, a Taino and Carib (West Indies natives) storm god. The Spanish modified the word to hurricane, and it is now used to describe Atlantic and Eastern Pacific storms that meet hurricane criteria.

Historically, Puerto Rico has suffered damage from hurricanes, notably Betsy in 1956 and Hugo, in 1989. Betsy destroyed 15,000 homes in Puerto Rico and caused 16 deaths. Both Betsy and Hugo started as tropical waves off the African Coast. Puerto Rico has been spared in recent years, although it has had several close calls, in particular Gonzalo in 2014.

The 2015 tropical storm season will probably be considered relatively quiet as no major storms struck the US mainland. Tropical waves and depressions formed but strong winds aloft created shearing forces which prevented storm formation. These shearing winds are a feature of El Nino events, and explain in part why hurricane activity diminishes during El Ninos, a condition we’re in right now. The winds counteract the effects of warmer than usual surface waters which act to promote storm formation by providing energy to the developing storm. By the way, the information I present here has been distilled from the excellent blog entries of Dr. Jeff Masters, of the Weather Undergound, at www.wunderground.com. Refer to his entries for detailed and lucid explanations of these complex events.

Map showing surface temperature excursions during September, 2015. Note especially the warm temperatures (indicated by shades of red) in the Atlantic off Florida, the Pacific off Mexico, and the Arabian Sea.

To think the 2015 hurricane season was uneventful represents a mainland-centric and thus skewed version of this season’s meteorology. There were in fact several remarkable weather events this season. Hurricane Fred struck the Cape Verde islands, close to the coast of Africa, at the end of August. The last time that occurred was in 1892. The islands (now more properly known as the Republic of Cabo Verde) are desert like, with average annual rainfall of about 10 inches. Fred delivered about that much rain in a day, thus causing extensive flooding.

The shearing winds died down in late September and Tropical Storm Joaquin grew explosively into a Category 3 hurricane. From the very beginning, Joaquin was unusual. Eighty-five per cent of strong Atlantic hurricanes originate with low pressure waves off of Africa – Joaquin did not. Joaquin apparently started as a wave off the South Carolina coast that established a warm-core tropical cyclone northeast of the Leeward Islands. This area is normally too far north and therefore too cold to produce strong tropical cyclones. This year, the warmer than normal surface water temperatures (see the temperature figure, above) allowed for storm development.

And it is not just surface water temperatures that are important. The cyclonic winds churn the waters and cause surface waters to sink, and deeper waters (perhaps to 50 meters in depth) to come to the surface. Since these deeper waters are now as warm as the surface, a brewing storm gains energy, allowing it to intensify.

Hurricane Joaquin, October 2, as photographed from the International Space Station. The lights at the top of the image are Miami and Miami Beach.

Joaquin intensified rapidly, going from a Category 1 storm (85 mph sustained winds) to a Category 3 (115 mph) in only six hours. The day before (Tuesday, September 29), the top winds were only 70 mph. Joaquin thus became the second major hurricane of the season (Danny was the first), unusual for a strong El Nino year. By October 3, Joaquin had grown into a Category 5 storm, also unusual in an El Nino year.

The rapid intensification led to a tragedy related to Puerto Rico. The container ship El Faro left Jacksonville early in the morning of September 30, on her way to San Juan. At that time, Joaquin was a tropical storm, with top winds of 70 mph, expected to grow in to a minimal Category 1 storm centered in the Bahamas. El Faro’s course would take it with 200 miles of Joaquin, with expected winds of 35 mph and 10 feet seas. Joaquin intensified rapidly and the El Faro, for some reason without power, found herself, in the morning of October 1, right in the northwest eyewall. The El Faro sank with all hands (28 Americans and 5 Poles); the Coast Guard yesterday (October 30) located her hull and hopes to retrieve her data recorder soon.

Joaquin contributed to, but did not cause, exceptionally heavy rainfalls- 20 inches or more in a 2 to 3 day period – and consequent severe flooding in South Carolina. These rains actually resulted from a Nor’easter fed by copious amount of moisture from the warm off shore waters.

On Tuesday, October 20, Tropical Depression 20-E formed in the Pacific, 445 miles east-southeast of Acapulco, Mexico, under conditions of light wind shear, warm waters (86 F) and a moist atmosphere. While poorly organized at first, TD-20-E was in ideal circumstances for rapid intensification. This in fact happened. TD-20-E morphed into Hurricane Patricia and became the fastest intensifying Western Hemisphere hurricane ever observed. Her central pressure was 980 mb (mb -millibar – a unit of atmospheric pressure. Typical atmosphere pressure is about 1,000 mb) at 5 am Thursday, October 22, and 880 mb 24 hours later – an astonishing drop of 100 mb in one day. Her winds intensified by 100 mph in 24 hours, from tropical storm to a Category 5 hurricane. By the next day, Patricia’s pressure was measured at 879 mb, with sustained winds of 200 mph, maintained for twelve hours. This was the lowest pressure ever observed in an Eastern Pacific hurricane, and also the highest reliably measured wind speeds for a tropical cyclone anywhere on earth.

MODIS satellite image of Hurricane Patricia, October 22. Patricia was a Category 4 storm at that time.

Fortunately, Patricia struck the Mexican Pacific coast in a rugged, relatively unpopulated area and dissipated its energy in the mountains of Central Mexico. As a tropical depression, she carried moisture into Texas and added to an already wet month. In fact, the Dallas – Fort Worth area recorded one of the wettest Octobers on record, with over 20 inches of rain. Remnants of Patricia were sufficiently strong so as to generate strong wind warnings and heavy rains in Upstate New York, and cause wind-related delays at Newark and other east coast airports as late as October 27 and 28.

As I write this (November 1), another very rare event is occurring – a Category 4 tropical storm in the Arabian Sea, heading for the Yemen coast. Tropical Cyclone Chapala, the second strongest storm on record for the Arabian Sea, is a rare event because the Arabian Sea is small, with a short tropical storm season, May – early June, and then late October through November, on either end of the Southwest Monsoon. Furthermore, typically high wind shears and dry air from the Middle East deserts hinder storm formation. Tropical Cyclone Chapala will be only the third cyclone to hit Yemen since the 1960s.Coastal Yemen typically gets about two inches of rain per year. Even the mountains there get only about 10 inches per year. Chapala will likely deliver several years’ worth of rain in a short time. Destructive flooding is a distinct possibility. If landfall is near the mouth of the Gulf of Aden, as expected, maritime commerce (400 ships per day pass through the Gulf of Aden) will be affected.

Tropical Cyclone Chapala nearing Yemen, October 31, 2015.

Quiet year in the Atlantic? I don’t think so. Consider:
• Hurricane Fred striking the Cape Verde islands.
• Two strong hurricanes in the Atlantic (Danny and Joaquin), rare for an El Nino year.
• The strange genesis of Hurricane Joaquin, near the Leeward Islands, and its rapid intensification to a Category 5 storm, again rare for an El Nino year.
• The huge rainfall event in South Carolina, and
• The exceptional rainfall totals in Texas, both in May and again in October.

Add to that the rapid intensification of and amazingly powerful Hurricane Patricia and the most unusual Tropical Cyclone Chapala. And did I mention the unusually large number of hurricanes near Hawaii this year? Or the very active Pacific typhoon season? The record heat in South Africa? The drought-induced wildfires in Indonesia, and the US west?

Last February, during a cold spell in Washington, James Imhofe, Republican from Oklahoma, tossed a snowball onto the floor of the US Senate and offered it as part of his case for why global warming is a hoax. Imhofe is the author of the book The Greatest Hoax: How the Global Warming Conspiracy Threatens Your Future.

I would have to believe, if Senator Imhofe were to read this blog entry, even he would be impressed. Probably not. I suspect Senator Imhofe suffers from epistemic closure: one who lives in a bubble into which inconvenient facts can’t penetrate.

I think it was Mark Twain who wrote “Reader, suppose you were an idiot. And suppose you were a member of Congress. But I repeat myself.”

Notes: As noted in the text, most of the information here has been taken from Dr. Jeff Master’s blog entries on www.wunderground.com.

The three storms in the top image are three named storms in the Pacific -Kilo, Ignacio and Jimena, in August 2015. Three named storms at one time is unusual.