Tropical cyclone Gamede

Remember this storm from two or three weeks back? The South African weatherservice has written an article on its impact, which I take the liberty of reproducing here.

The names of many tropical cyclones are forgotten as soon as the season is over - there is a lot of sea in the South-West Indian Ocean and hopefully mariners will have heeded the warnings (this is not always the case - see below).

Figure1 : Track Chart for Tropical Cyclone ‘Gamede’

However, the name of 'Gamede' will be remembered by many. Refer to the track chart in figure 1 :

• St Brandon is an archipelago belonging to Mauritius. Unfortunately 'Gamede' had intensified to 'Tropical Cyclone' category (Hurricane Force winds - i.e. sustained speeds in excess of 116 km/ hr) - just prior to passing over the islands on 23 February. The weather station on Île Raphael reported SE'ly winds of over 90km/ hr in the morning. By 12h00 UTC the pressure had dropped to 957 hPa as the eye passed within less than 50 km of the island. No damage reports are available.
• the Meteorological Service of Mauritius put the Island on red alert on the 24th, the first time this season. Sadly, some people chose to ignore the warnings and there were two deaths - even though the worst of the weather remained to the north-west. Police had to force overly-keen wind surfers and surfers out of the water...
• on La Réunion (which holds several global rainfall records) over 2000mm was recorded in some places in the mountainous interior. A bridge was washed away, causing damage of about R150m. Fortunately 'Gamede' reached the 'Intense Tropical Cyclone' stage (sustained wind speeds in excess of 142 km/ hr) when it was furthest from La Réunion, to the north-west. Nevertheless, gusts of over 200km/ hr were recorded near some exposed cliff faces.
• despite the 6-hourly warnings prepared by the Tropical Cyclone Centre on La Réunion - which are broadcast to all ships via the Global Maritime Distress and Safety System (GMDSS) - some vessels did not escape the storm. M/V Spirit of Adventure with 250 passengers on board suffered broken windows and other damage and had to run for Antsiranana. The Maltese-registered general cargo vessel 'Gracia' (24 199 tons gross) also got too close to the cyclone, but in this case the crew decided they'd be better off in the life raft and abandoned ship. They were rescued and taken to Durban. It is still not clear what has happened to the vessel - if it is still afloat it could end up in the Agulhas Current !
• on Friday 2 March a heavy easterly swell arrived on the beaches of northern KwaZulu-Natal, courtesy Tropical Cyclone 'Gamede'. They had been travelling for roughly 2 days (15 sec period -> 22 kts group speed - distance ~ 1000 nm) For the first time in over 4 years Lake St Lucia was opened up to the sea. See accompanying Landsat image. On this day the estuary mouth was not open - the coastal sediment is due to seepage. Apparently the crocs had a fine time welcoming the incoming salt-water fish!
• unfortunately the high swell that subsequently hit the Durban beaches was more prolonged due to 'Gamede' having been blocked by a high pressure ridge to the south. Coming in with a near spring high tide, the waves flooded the lower Marine Parade and covered the road in sand. Beaches had to be closed due to the shark nets being tangled up by the heavy seas.

The port of Durban was closed at midnight on Friday and only re-opened to all vessels on Sunday. This is a good example of a case where an accurate forecast of sea state could well have saved significant amounts of time and money, by allowing port authorities and ship operators to plan a few days ahead. Unfortunately at this stage, the forecasting by numerical prediction models of waves generated by tropical cyclones is not as accurate as that for swell coming from the deep mid-latitude lows well to the south-west of the country.

Figure 2 : Satellite image of Tropical Cyclone ‘Gamede’ – ex Aqua/ MODIS

Figure 3 : Landsat 7 Advanced Thematic Mapper image of the southern part of the Greater St Lucia Wetland Park – a UN designated World Heritage Site

Ian Hunter
SOUTH AFRICAN WEATHER SERVICE