After an extensive lull of visually appealing thunderstorm activity, Cape
Tropical storm Irina is currently located off the east coast of South Africa and as can be expected, the storm remains fairly weak, this is mainly due to the fact that the water temperatures as far south as tropical storm Irina is, are less conductive for strengthening than further north. I think it’s important for people to realize though, that judging by the latest official forecasts, that this storm is not by any means over for South Africa and the main impact looks like it will take place later this week, with the brunt of the storm likely being felt on Friday into the weekend.
Irina is forecast to weaken further over the next day or two and weaken down to a 30kt depression, whereafter it is forecast to begin moving further north and to the west again where it will begin to re-intensify and is once again forecast to become a tropical cyclone before making landfall on late Thursday into Friday in extreme southern Mozambique. This storm has a history for remaining weaker than forecast, so it’s quite possible that it will never reach tropical cyclone strength, but those in the path of it, at least for now, should prepare for one. The forecast windspeed at landfall at present is 70kt with higher gusts. The increase in strength in days 3-4 is due to an increase in sea surface temperatures as well as increased upper level divergence and lower wind shear.
The area of heavy rainfall associated with Irina looks to become far more concentrated with the latest GFS model run, showing very heavy rains but only within the direct landfall area of the storm. The surrounding areas, it’s showing only light to moderate rainfall for the most part, though this of course is subject to change.
It is important to discuss the alternate scenarios as forecast by the models. While the official forecast agencies have currently forecast a landfall to take place, the ECMWF (EURO) model forecasts another weakness in the ridge as we get into the latter parts of the weekend, this would move tropical storm Irina south again as it approaches the coast, but then move it to the south east. Should this scenario occur, there is a chance that far less effects of Irina will be felt than is forecast. I will be keeping an eye on both the GFS and the EURO and see if they continue to differ or if one follows the other’s scenario.
Over the weekend tropical storm Irina caused severe flooding in parts of KZN with 24 hour totals in places receiving in excess of 200mm. The Durban beaches were closed, as large swell up to 6 meters pounded the KZN coastline and hundreds of houses were flooded. The break along the Durban coastline showed just why fatalities occur with these storms as many waves looked like a surfers dream.
The storm still very much warrants watching this week as another round of severe weather for South Africa is certainly possible, though as mentioned above, it’s also possible that the storm may move away without any landfall and thus restrict the damage and severity to rough seas.
A gallery of images of Irina can be found here: IOL IRINA GALLERY
For previous discussions on Irina, visit: Tropical Storm Irina
Update 5 March 2012 (14:00): Well once again the forecast has changed as the models changed. The official forecast seems to now be siding with the EURO model in forecasting the storm to continue looping and then fall victim to a weakness in the ridge to the south and end up heading eastwards again before making landfall. The system is more compact than it was over the weekend and this could mean that rainfall, if any, is limited. One can note that this change in track forecast also means a change in intensity forecast due to the cooler SSTs it will experience. The latest forecast now calls for the storm not to reach cyclone status once more!
Update 6 March 2012 (12:00): Tropical storm Irina remains weak off the east coast of South Africa with the new official forecasts from La Reunion and JTWC both calling for the storm to dissipate without making landfall over the next few days as it continues it’s loop. The GFS model shows the cyclone coming close to the KZN coast and even having an affect with heavy rain, but the official forecasts and the other models do not show this. It looks like Irina should slowly fizzle out in the week.
Update 7 March 2012 (08:00): Irina is not done yet. Once again there is a twist in the tale, and quite frankly, this is starting to get a little frustrating. Just as one thinks they have the storm pegged, the forecast upper air pattern changes and as does the forecast track. The latest model runs are showing tropical storm Irina remaining fairly weak with winds between 35kt and 50kt over the next few days, but they are once again showing landfall taking place! Landfall is now forecast for next Tuesday in Mozambique as a weak tropical depression. The latest forecast and model runs also show the weak storm coming very close to South Africa once again, bringing with it the potential of some moderate to heavy rain for KZN between day 4 and 6 primarily. As with every forecast, all there is to go on is the upper air dynamics and what the models are suggesting may happen and the reason for the inconsistent forecasts are because the models keep depicting different synoptic conditions. Irina still warrants keeping an eye on, even though the chances for destruction have greatly diminished since last week, the potential for flooding has increased since Monday. A tropical depression has weak winds, but can still dump a lot of rain, though the models are currently suggesting bulk of the rainfall will fall over the ocean before becoming a bit ‘drier’ prior to landfall. These things as I’m sure everyone realizes now, can change at any time though.
Update 9 March 2012 (08:00): Irina has weakened over the past couple of days and is now a tropical depression with winds between 50 and 60km/h, so equivalent to a typical Cape Town cold front in the winter. The storm is forecast to weaken further as it moves west and then north-west, making landfall as a big pile of rain in a few days. It looks unlikely now that the storm will have an impact on South African weather and I think the guard can be let down, it would need to do something very special to cause problems here from it’s current position and strength. Of course if you were planning a weekend just off the southern Mozambique coast, you can expect unpleasant conditions.