Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.4.7.3 Wind ====

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'''Mean wind speed:''' Scarcity of observations limits assessment of long-term changes in winds over the small islands in the Pacific and CAR. Records indicate that average daily wind speeds have slowly declined in Hawaii, but have remained constant across western and southern Pacific sites since the mid-20th century ( [[#Marra--2017|Marra and Kruk, 2017]] ). Recent studies of reanalyses and hindcast simulations indicate an intensification of the Pacific trade winds during the 1992–2011 period, which contributed to the ocean cooling in the tropical central and eastern Pacific ( [[#England--2014|England et al., 2014]] ; [[#Takahashi--2016|Takahashi and Watanabe, 2016]] ). Projections estimate up to 0.4 m s <sup>–1</sup> (8%) increase in annual winds in CAR under RCP8.5, which is associated with changes in the extension of the North Atlantic Subtropical High that enhances the Caribbean low-level jet during the wet season, and stronger local easterlies due to enhanced land–ocean temperature differences in the dry season ( [[#Costoya--2019|Costoya et al., 2019]] ) ( ''low confidence'' ).

'''Tropical cyclone:''' Tropical cyclones have devastating impacts on the small islands due to intense winds, storm surge and rainfall, although the associated rainfall can also be beneficial for freshwater resources. It is ''likely'' that tropical cyclone intensity and intensification rates at a global scale have increased in the past 40 years but it is not clear if regional-scale changes are basin-wide or due to shifts in tropical cyclone tracks ( [[IPCC:Wg1:Chapter:Chapter-11#11.7.1.2|Section 11.7.1.2]] ). Other, less data-sensitive tropical cyclone features, such as the poleward migration of where tropical cyclones reach peak intensity in the western North Pacific since the 1940s ( '''medium confidence''' ) and the slowdown in tropical cyclone translational speed over contiguous USA since 1900 ( '''medium confidence''' ), can affect rainfall and flooding over small islands in CAR and the Pacific ( [[IPCC:Wg1:Chapter:Chapter-11#11.7.1.2|Section 11.7.1.2]] ).

Projections of global changes in tropical cyclones indicate more frequent Category 4–5 storms ( ''high confidence'' ) and increased rain rates ( ''high confidence'' ) ( [[#Knutson--2020|Knutson et al., 2020]] ), with relative sea level rise exacerbating storm surge potential, but with large regional differences (see [[IPCC:Wg1:Chapter:Chapter-11#11.7.1.5|Section 11.7.1.5]] ). By the late 21st century, tropical cyclones are projected to be less frequent in the basins of the western and eastern North Pacific, Bay of Bengal, Caribbean Sea and in the Southern Hemisphere, but will be more frequent in the subtropical central Pacific ( [[#Murakami--2014|Murakami et al., 2014]] ; [[#Yoshida--2017|Yoshida et al., 2017]] ; [[#Bell--2019|Bell et al., 2019]] ; [[#Knutson--2020|Knutson et al., 2020]] ). Over CAR, tropical cyclone intensity is expected to increase by the end of the century under RCP8.5 due to higher sea surface temperatures but can be inhibited by increases in vertical wind shear in the region ( ''medium confidence'' ) ( [[#Kossin--2017|Kossin, 2017]] ; [[#Ting--2019|Ting et al., 2019]] ). The poleward movement of the area in which tropical cyclones reach peak intensity in the western North Pacific is ''likely'' to continue, which affects the tropical cyclone frequency over the small islands in the area ( [[IPCC:Wg1:Chapter:Chapter-11#11.7.1.5|Section 11.7.1.5]] ; [[#Kossin--2016|Kossin et al., 2016]] ). Projections also indicate an increase (decrease) in the tropical cyclone frequency during El Niño (La Niña) events in the Pacific at the end of the 21st century ( [[#Chand--2017|Chand et al., 2017]] ). RCP8.5 2080–2099 projections indicate a 2% increase in the number of tropical cyclones in the north-central Pacific relative to 1980–1999, with tracks shifting northward towards Hawaii (N. [[#Li--2018|]] [[#Li--2018|]] [[#Li--2018|]] [[#Li--2018|]] [[#Li--2018|Li et al., 2018]] ). Given projected reductions to the overall number of tropical cyclones but increases in storm intensity, total rainfall and storm surge potential, we assess ''medium confidence'' of overall changes to tropical cyclones affecting the Caribbean and Pacific small islands.

'''Projections indicate that small islands will generally face fewer but more intense tropical cyclones''' ( medium confidence ''') although there is substantial variability across small island regions given projected regional shifts in storm tracks.'''

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