Tropical Cyclone Tauktae recently impacted India, making landfall in Gujarat on 17th May 2021 after passing along the wester coast of India. Floodlist reports that weather stations in Mumbair recorded 230mm of rain in the 24 hours to 18th May, which is reportedly the highest 24-hour rainfall total recorded in Mumbai in May. The rainfall from this event is very extreme for this time of year. Impacts have been severe, with fatalities in 4 states and ~7000 homes damaged with more than 200,000 people evacuated.
ECMWF's extended-range tropical storm and strike probability forecast products first began to indicate the likelihood of a tropical system forming in the Arabian Sea from the 22nd April, 3 weeks before the genesis of the storm on 14th May. The tropical storm strike probability (including genesis) map from 22nd April 2021 is shown below, valid for the week of 17-23rd May 2021. This predictability is likely due to the active Madden-Julian Oscillation (MJO) over the Indian Ocean, which can impact the likelihood of tropical cyclones occurring in the region, and is also linked to the development of Tropical Cyclone Yaas in the Bay of Bengal on 23rd May. Extended-range forecasts from 6th May also indicated the potential for tropical storm formation in the Bay of Bengal. The MJO phase diagram below shows the extended-range forecast from 29th April, indicating the MJO to remain active over the Indian Ocean over the coming weeks. It is worth noting that the signal is likely dampened in such phase diagrams during the transition of the ENSO state from La Nina to neutral conditions during the previous months, as the calculation of the MJO index includes removal of the previous 120-day mean of the relevant variables.
Images: Left, weekly mean tropical storm strike probability forecast from 22nd April 2021, valid for 600-768hours (17-23 May). Centre, MJO extended-range forecast from 29th April 2021. Right, satellite image via NASA worldview of TC Tauktae approaching landfall on 16th May 2021.