| Summary: | <p>This article analyzes the relationship between off-season
tropical cyclone (TC) frequency and climate variability and change for the
Pacific Ocean and Atlantic Ocean basins. TC track data were used to extract the
off-season storms for the 1900–2019 period. TC counts were aggregated by
decade, and the number of storms for the first 6 decades (presatellite
era) was adjusted. Mann–Kendall nonparametric tests were used to identify
trends in decadal TC counts and multiple linear regression (MLR) models were
used to test if climatic variability or climate change factors explained the
trends in off-season storms. MLR stepwise procedures were implemented to
identify the climate variability and change factors that explained most of
the variability in off-season TC frequency. A total of 713 TCs were
identified as occurring earlier or later than their peak seasons, most
during the month of May and in the West Pacific and South Pacific basins.
The East Pacific (EP), North Atlantic (NA) and West Pacific (WP) basins
exhibit significant increasing trends in decadal off-season TC frequency.
MLR results show that trends in sea surface temperature, global mean surface
temperature and cloud cover explain most of the increasing trend in decadal
off-season TC counts in the EP, NA and WP basins. Stepwise MLR results also
identified climate change variables as the dominant forces behind increasing
trends in off-season TC decadal counts, yet they also showed that climate
variability factors like El Niño–Southern Oscillation, the Atlantic
Multidecadal Oscillation and the Interdecadal Pacific Oscillation also
account for a portion of the variability.</p>
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