Yet Another Tropical Cyclone Hits Yemen

UPDATE: 1200Z Sunday 8th November

Tropical Cyclone Megh intensified overnight and at 0900Z the JTWC had its intensity at 110 gusting 135 knots (204 gusting 250 kph). The eye has just passed over the northern part of the island of Socotra, as shown by the latest 1-km visible image (1130Z) and a 85 GHz microwave image at 1039Z. Earlier satellite-derived precipitation rates were around 1.2 inches (30 mm) per hour.

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20151108.0313.f18.x.rain.05AMEGH.90kts-956mb-127N-561E.60pc

Original article:

Tropical Cyclone 05A (Megh) is the second storm to hit Yemen in a week. For a country that has almost no rainfall at all in some areas, Yemen has been awash of late. First was Tropical Cyclone Chapala earlier this week, which claimed several lives and completely buried some villages in floods. This week it is Tropical Cyclone Megh, the fifth such storm in the Indian Ocean this year and the second in the Arabian Sea, an area that rarely sees these events. Megh will hit the island of Socotra tomorrow before continuing on to clip the Somalian horn and then into the Gulf of Aden again.

The reason why these two cyclones – called hurricanes in the Atlantic and Eastern Pacific – formed is down to a combination of record warm ocean heat-content in the Indian Ocean and Phase 3 of the Madden-Julian Oscillation (MJO), a regular pulse of convective activity that moves from west to east around the globe every 30-60 days.
The MJO has a large effect on tropical activity, with areas ahead and behind of it relatively quiet as areas in between see more in the way of thunderstorms and cyclones . The warmer Indian Ocean seems to be a trend that has evolved in the past decade, with the Pacific Ocean losing its and it showing up in the Indian Ocean. This process has accounted for up to 70% of the global upper ocean (top 700 m) heat gain in the past decade (see this paper).

MJO over the past 40 days. The blue line shows the latest status, with a relatively strong Phase-3 signal in the Indian Ocean, moving eastwards. Image from the Australian Bureau of Meteorology.
MJO over the past 40 days. The blue line shows the latest status, with a relatively strong Phase-3 signal in the Indian Ocean, moving eastwards. Image from the Australian Bureau of Meteorology.
Sea-surface temperatures (SST) in the Indian Ocean. SST is important, but it is the depth of the heat that is most important in supplying sufficient energy to a tropical system (see below). Image from NOAA/AOML
The depth of the 26 °C isotherm should be at least 50 metres for strong intensification of tropical storms.
Tropcial Cyclone Heat Potential depends on both the temperature and depth of warm water. Values of above ~50 kJ/cm² can lead to rapid intensification, if other factors are also favourable (low shear, deep moisture).

The current El Niño Modoki – also a relatively newly-observed trend – is a phenomenon in which the warmest El Niño waters are now showing up more in the central Pacific instead of the more eastern waters. This causes the western and eastern Pacific to be cooler than the centre, and this has probably contributed to the warmer Indian Ocean as well. With this effect still poorly understood it remains to be seen what effect it will have on the coming winter, as forecasts predict it to last well into the new year.

Schematic of the El Niño Modoki phenomenon, which shows up as warm anomalies in the central rather than the eastern Pacific waters. Image from Jamstec

Whatever all the above science means, it is of little comfort to the people of Socotra who, still recovering from Chapala’s drenching last week, now have to face a similar ordeal tomorrow as Megh scores a direct hit with 85-knot winds and more torrential rainfall.

Latest forecast from the Joint Typhoon Warning Center.
Latest forecast from the Joint Typhoon Warning Center.
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