This useful information from Des Cason, based in SA, who offers advice to cruisers visiting the country and routing and weather information for the Indian Ocean. E-mail at sygambit@gmail.com

On average this area gets 5-9 cyclone annually (some years more and some less) and these have to be differentiated between those that originate south of Chagos (BIOT) and those that develop in the Mozambique Channel south of Mayotte.

The Chagos cyclone as a rule track W/SW and usually hit the east coast of Madagascar and then re-curve back SE crossing Mauritius and Reunion. Very seldom do they actually cross Mada and get into the channel between Mada and Mozambique. The stats on these events are freely available and most yachties would be aware of this pattern.

What they are usually not aware of is the incidence of the formation of RTS (Revolving Tropical Storms) in the Moz channel south of Mayotte. On average they occur 5 times a year and have their origins south of Mayotte in the region off Nacala in Moz and then move down the channel and after making a few detours invariably with a very erratic pattern usually, head SE and clip the southern tip of Mada and trash Toliara on the SW coast of Mada. Whilst not as a rule classified as true cyclones they have been known to have sustained wind speeds of 45-50kts+ and typically torrential rain which is due to the system being trapped between the two land masses and the warm current to feed off.

Those yachts who elect to go via the northern route around the top of Mada and then down the Moz channel should be aware that they could be exposed to this pattern from Nov and peaking in Feb when Moz as regular as clockwork has torrential rains and floods in the Xai-Xai/Inhambane area.