# Climate Perspectives in the Intra-Americas Seas
## 3 Regional Climate Features
### Moisture Transport  
Moisture transport in the IAS is often discussed in terms of the WNAM [107], where rainfall is favoured by moisture transport from the Gulf of Mexico, with the eastern tropical Pacific,Caribbean Sea, and the Gulf of Mexico playing a minor role [108]. An accurate quantification of evapotranspiration and moisture recycling is constrained by the complex surface and observational data availability [109; 110]. Moisture source diagnostics, related to the NAM and WNAM, have been performed using observations [111], reanalysis, [112], modelling [113], and the combination of water vapour tracers-enabled models and water-stable isotopes [4; 114]. Despite the association of the IAS for WNAM development, based on the connection between the GPLIJ and the CLIJ, the IAS waters also play a key role. Complimentarily, here, we focus in moisture transport over the IAS. Figure 3A shows the maximum of vertically integrated water vapour during the rainiest period of the year, which reduces during the dry season despite still maintaining a good amount of moisture in the southernmost part of the IAS (Figure 3B). The mechanisms for regional moisture transport have long been explored. A northward transport of moisture across the 20\({}^{\circ}\) N latitude with a southward shift of minimum moisture transport during the boreal autumn was identified in Reference [115]. The results of previous studies have highlighted the relevance of LLJs and the ITCZ to modulate moisture transport and rainfall [116]. The Caribbean Sea is the main source of moisture for Central American rainfall, whilst concurrently modulating regional moisture transport dynamics. Transport from this source is very efficient and transport peaks between 4 to 6 days [79]. An independent analysis of moisture transport using physical tracers [117] showed consistency of previous backward trajectories and vertical integrated moisture flux-based analysis. The Caribbean Sea contributes to rainfall in northern South America with descending flow from the CLLJ that connects to a low-level structure in the Venezuelan plains [101; 102]. Continental sources of moisture for Central America are identified as local moisture recycling and northern Colombia, with the latter allowing connectivity with the Amazon to enhance inter-hemispheric bridges. However, the quantification of local evapotranspiration and its role in recycling remains an open problem, limited by data scarcity and surface complexity. Moisture transport is sensitive to the variability modes that drive changes in the SST and LLJs. The moisture supply response to the ENSO is modulated by the response of the CLLJ and the Choco jet, so that moisture supply decreases (increases) from the Caribbean (eastern tropical Pacific, ETPac) during the first stage of the rainy season. It is then enhanced from the Caribbean between July and September and decreases from the ETPac in August [79]. The role of anomalous moisture transport during ENSO events has also been confirmed by changes observed using modelling [118] and physical tracers [119]. The effect of the North Atlantic Oscillation (NAO) has been suggested to have a more significant impact on the structure of moisture transport directly acting over the CLLJ rather than the intensity of moisture sources in the Caribbean. This has an overall effect of increasing transport to Central America during NAO negative phases. In this sense, the location at which the maximum transport arrives is also modulated by NAO-induced variations. At lower frequencies, the impact of  
Figure 3: Mean total column water vapour (shaded) and the vertically integrated water vapour flux (arrows) for (**A**) May–October and (**B**) November–April for the 1979–2019 period based on ERA–5 data. A high moisture content was observed between May and October with transport mostly directed along the storm track, following the development of the meridional branch of the CLLJ. In contrast, a reduced moisture content is featured in the November–April period.