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[1] Using International Best Track Archive for Climate Stewardship (IBTrACS, version v03r03) analysis during satellite era we determined the trends of intensification of tropical cyclones (TC) over all the global basins, except the North Indian Ocean. Over all the basins, the rate of TC intensification from 64 kt to first peak of intensity maxima (global average value = 104 kt) was found to be positive. The above trends were significant for 4 out of 5 basins, except the North West Pacific. The trends indicate that the TCs now intensify from 64 kt to 104 kt nearly 9 hours earlier than they did 25 years back. The maximum reduction in intensification time is noticed over the North Atlantic Ocean where the average time needed for TC to intensify from 64 kt to 112 kt has reduced by nearly 20 hours during the past 25-year period.

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[1] Observations of 408 monsoon low-pressure systems (MLPSs) including 196 monsoon depressions (MDs) that formed in the Bay of Bengal during the 1951-2007 period, and the gridded analysis of daily rainfall fields for the same period, were used to identify the association of antecedent rainfall (1 week average rainfall prior to the genesis of MLPS) with the genesis of MLPS and length of inland penetration by MDs. Prestorm rainfall is treated as a surrogate to prestorm ground wetness conditions due to unavailability of historical soil-moisture data over the monsoon region. These observations were analyzed using self-organizing maps (SOMs) to group nine different prestorm monsoon rainfall patterns into different transition states like active, active-to-break, break-to-active, break, etc. The analysis indicates that MLPS are four times more likely to form on a day during active monsoon state compared to break state. Analysis of MLPSs linked to each monsoon state represented by SOM nodes shows that MDs with higher inland penetration were associated with higher antecedent rainfall. On the other hand, there was no significant difference in low-level atmospheric circulation for MDs with shortest and longest inland penetration.

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