Cyclone Chapala a Rare, Destructive Landfall in Yemen

Cyclone Chapala made an extremely rare landfall along the Gulf of Aden coast of Yemen Tuesday, triggering massive rainfall flooding in a desert location unaccustomed to tropical cyclone landfalls. 

According to the India Meteorological Department, the agency sanctioned by the World Meteorological Organization for issuing official tropical cyclone bulletins for the Arabian Sea, the center of Chapala made landfall about 44 miles (71 kilometers) southwest of Al Mukalla, Yemen, as of 7 a.m. Tuesday Yemen time.

At that time, IMD estimated the cyclone's maximum sustained winds from 75-80 mph (120-130 kph), a Category 1 equivalent storm on the Saffir-Simpson Hurricane Wind Scale, the first such intensity landfall in southern Yemen in at least 55 years. (More on the historical perspective is below.)

Chapala's core of hurricane-force winds passed near, or just west of Yemen's fifth largest city, the coastal, war-ravaged port of Al Mukalla, with a population of roughly 300,000.

IMD promptly downgraded Chapala to a tropical storm in the hours immediately after landfall.

While battering waves and coastal flooding hammered the coast, perhaps the most severe impact in Yemen was due to torrential rainfall.

Yearly Rainfall in 1-2 Days

Despite Chapala's weakening prior to landfall, torrential rain triggered major flooding in parts of Yemen.

(MORE: Cyclone Chapala Lashes Socotra with Flooding, Damaging Winds)

Social media photos showed feet of fast-moving flood water inundating parts of the city of Al Mukalla, as well as surrounding areas.

Furthermore, the south coast of Yemen is fronted by hills and mountains. 

Rivers running from these mountains that are normally dry, known locally as wadis, saw rapid rises with rainfall of this magnitude, with destructive mudslides and debris flows.

Persistent rainbands from Chapala slamming into those mountains may have produced rainfall totals over 200 millimeters (about 7.87 inches) in just 24 hours, according to satellite rainfall estimates from NOAA.

A separate NASA-IMERG satellite analysis estimated 12-20 inches of rain soaked Socotra Island, while 5-15 inches of rain fell in southern coastal Yemen near the landfall of Chapala's center.

This is over 2 to 7 times the average yearly rain in just a day or two over parts of south coastal Yemen. Average rainfall along the southern Yemeni coast is 2 inches (50 millimeters) or less, according to the University of Texas' Perry-Castañeda Library Map Collection.

We may never know, however, exactly how much rain falls or how strong the winds blew with Chapala. Yemen has been beset by violent conflict in recent years, disrupting the electrical grid and communication networks across the country. As a result, weather observations most of us take for granted are nearly non-existent.

Yemen has eight official synoptic weather observation sites, charged with reporting weather conditions at least once every six hours. Each site should have submitted 124 six-hourly reports in October, but six of them sent none at all, one site sent just one observation, and the other eked out just 13 of its 124 required reports.

Furthermore, much of the region expected to take a direct hit is already in the midst of a humanitarian crisis. According to the United Nations, the area expected to take a direct hit (the governorate of Hadramaut) is already at "crisis" level, with 106,900 residents displaced by war and conflict.

Most of the areas to the west of Hadramaut are classified in an even more dire "emergency" status, with widespread food shortages and more than 2 million people displaced from their homes. More than 500,000 children are believed to be at risk of severe acute malnutrition, according to the U.N.

(MORE: Why Tropical Cyclones Are Named)

Unprecedented Landfall?

You may wonder how often "tropical cyclone" and the "Arabian Peninsula" appear in the same sentence. How unusual was Chapala?

Hurricane specialist Michael Lowry says the head of the Cyclone Warning Division at the India Meteorological Department cited two "severe cyclonic storms" - those with winds of at least 55 mph - made landfall in Yemen in May 1959 and May 1960. 

Weather Underground's Dr. Jeff Masters says Tropical Depression Three in 2008 claimed 90 lives and was responsible for $400 million in damage. 

Secondly, there is no record of a cyclone of Category 4 strength or stronger tracking as far south as Chapala in the Arabian Sea.

It had rapidly intensified to a high-end Category 4 early Friday and remained in that Category through most of Saturday. This made Chapala the strongest tropical cyclone so far south in the Arabian Sea on record.

While direct measurements from reconnaissance aircraft are not available over the Arabian Sea, Chapala's rate of intensification from a high-end tropical storm to a high-end Category 4 storm in 24 hours ending 2 a.m. EDT Friday morning (80 knots of estimated wind speed rise) was quite impressive for this part of the world.

Warmer-than-average Arabian Sea water along its path along with an impressive pipeline of winds exhausting the top of Chapala's circulation allowed for Chapala to intensify so rapidly.

(MORE: Hurricanes in Strange Places | Strange Things in the Tropics in 2015)

Despite all this, Arabian Sea tropical cyclones are not as unusual as they sound.

Each year, an average of one to two tropical cyclones form in the Arabian Sea, according to a 2011 climatology study by Amato Evan and Suzana Camargo. 

These cyclones are most likely to form in two periods: from May through June and October through November. The mid-late summer period is typically not favorable, thanks to increased wind shear from the wet phase of the Asian monsoon. 

(MORE: Where the Season Peaks Twice)

In June 2007, Cyclone Gonu was the most intense Arabian Sea storm on record, making landfall in Oman, then in southern Iran.

Gonu claimed 100 lives in Oman, Iran and the United Arab Emirates and was responsible for $4 billion in damage, according to the Evan and Camargo study.

Almost exactly three years later, Cyclone Phet alarmingly intensified to a Category 4 equivalent cyclone, before weakening to a Category 1 storm upon making landfall on the eastern tip of Oman, east of the capital city of Muscat. 

In May 1999, Cyclone ARB 01 slammed into Pakistan near Karachi as a strong Category 3 equivalent storm, killing at least 700 in Pakistan. This was the strongest tropical cyclone on record to hit Pakistan.

(MORE: Deadliest Tropical Cyclones in World History)

In the limited historical record, however, strong cyclones in the Arabian Sea are more rare than other basins, due to the proximity of dry air from the Arabian Desert, the aforementioned increased wind shear during the wet phase of the Asian monsoon, and the basin's overall small size.

MORE ON WEATHER.COM: Cyclone Chapala Photos, Images