Weather deteriorated rapidly over Mauritius during the night of 12 January 2013, with violent thunderstorms and heavy showers spreading over the island.
05 September 2022
12 January 2013
By Philippe Veerabadren (Mauritius Meteorological Services)
Around 17:00 UTC (21:00 LT) lightning was observed to the east of the island, over the sea. The lightning was spectacular, as it was quite frequent. Rain subsided from 05:00 UTC (09:00 LT) the next day.
On ECMWF upper air charts of 12 January (00:00 Z model run), a low was forecast to develop to the northeastern part of Mauritius, on the 500hPa level. In higher levels up to 200hPa the model was showing a deep trough oriented in the NW–SE direction and off the northeastern coast of the island.
The mid-tropospheric low seemed to have been cut off from a similar deep trough that was present at 500hPa earlier. This low was seen to be embedded in a cold pool.
The 12:00 UTC ECMWF model run of the same day forecast the low, with its cold mid-tropspheric air, to cross Mauritius on Saturday night into Sunday morning.
The cooling by about four degrees at 500hPa brought about a change in the lapse rate and contributed towards static instability of the atmosphere.
Models also expected the CAPE to reach a peak of 800 Joules/Kg at the time of crossing. Further model output of 18:00 UTC on 12 January, showed convergence at 700hPa and divergence at 200hPa and a highly negative vertical velocity between 600hPa and 150hPa.
The model was predicting high humidity from surface to reasonably high in the troposphere and even expecting saturation from 500 to 200hPa at 18:00 UTC on the 12th.
The moisture could be attributed to clouds advection, which could be seen from the satellite images at that time (Figures 1 and 2). The models were accurate and all these ingredients came together to produce the violent thunderstorms.
Further details about the event can be found in Philippe's research