The equivalent of a Category 4 hurricane but has since weakened to the strength of a Category 2 – Cyclone Chapala, should make landfall in Yemen on Tuesday. The outlandish prospect of a hurricane striking the desert, war-torn country of Yemen, on the southern tip of the Arabian peninsula, raises two questions. Has this ever happened before, and is climate change a contributing factor?
Fortunately for the coast, Chapala is forecast to weaken into the equivalent of a Category 2 hurricane before striking Yemen. While it should still bring damaging winds to the port city of Al Mukalla, Chapala’s primary threat should come from its potential to produce heavy rains. An area along the Yemen coast could receive 30 to 45 centimeters of rain during the next two days, certain to cause major flooding as that part of the country typically receives only about five centimeters of rain a year. The island of Socotra, off the coast of Yemen, was already reeling from the effects of high winds and rains on Monday.
Yemen has been struck by tropical cyclones, as they are known in the Indian basin, before. The equivalent of a weak tropical storm, Keila, hit the country in 2011. According to the India Meteorological Department, two cyclones with stronger winds hit Yemen in 1959 and 1960. It appears safe to conclude that the country hasn’t been hit by a storm this potentially devastating in nearly half a century.
In terms of climate change, it is not unusual for cyclones to form in the Arabian Sea. A research paper published in 2011 found that an average of one to two tropical cyclones form in the Arabian Sea each year, although most of these are not strong enough to be classified as severe cyclones.
Meteorologists typically measure cyclone strength by central pressure rather than maximum sustained winds. The lower the pressure at the center of a hurricane, the faster the air spiraling around the center must spin to offset the steeper gradient of the pressure surface. Chapala reached its peak intensity early Friday when its central pressure fell to 922 mb. In the Arabian Sea’s hurricane record only Cyclone Gonu, a 2007 super-cyclone that grazed Oman, had a lower central pressure, 920 mb.
Chapala is also notable because of where it formed and how quickly it intensified. No cyclone has become so strong so far south in the Arabian sea. Hurricanes can’t form or survive near the equator because the Coriolis force that allows them to develop tights centers of circulation is near zero there. Chapala has been moving westward across the Arabian Sea at a latitude of about 10 degrees North. Additionally according to satellite data, Chapala intensified from a strong tropical storm to the equivalent of a Category 4 hurricane in just 24 hours, ending Friday. That comes less than a month after Hurricane Patricia rapidly intensified from a tropical storm to a Category 5 hurricane in about 30 hours off the coast of Mexico in the Pacific Ocean.
No single weather event can be attributed to climate change, and it’s difficult to compare hurricanes now to those even three or four decades ago because of the advent of satellites and aircraft reconnaissance, which have allowed scientists to monitor storms much more continuously. However, warmer sea surface temperatures are consistent with stronger hurricanes and rapid intensification.
And while most computer modeling of activity in a warmer world suggests the number of hurricanes may not increase, it does indicate the very strongest of those that form will be a bit stronger than they would have otherwise.