## 3 Results
### Variability and Drivers
#### 3.3.3 Summer Season  
The EOF analyses were repeated for the summer season, when sea levels are at a maximum, using data for June through September. The monthly data were extracted and averaged annually, and EOFs were calculated before and after detrending. Figure 5 shows the PC1 spatial loadings and timeseries for the raw (SumPC1_raw) and detrended (SumPC1_detrended) summer data. Table 4b shows the correlations between the summer PC1 timeseries (raw and detrended) and the 10 indices. The summer season coincides with an intensification of the CLLJ [55], an eastward expansion of the Atlantic part of the western hemisphere warm pool [70], and a July intensification of sea level pressure [54]. These phenomena have a known seasonal influence on Caribbean summer climate, e.g., modulating the mid-summer drought [75; 33; 76]. Their association with an enhanced or diminished amplitude of the sea level summer maximum was examined.  
PC1 explains 50% and 33% of the raw and detrended data, respectively. For the raw data, the spatial pattern (Figure 5a) shows almost uniform loadings across the Caribbean south and east of Jamaica, suggesting a basin-wide response. The SumPC1_raw timeseries (Figure 5b) is dominated by a linear trend with interannual variability superimposed. It  
Figure 5: Spatial variability (**Left column**) and timeseries of principal components (**Right column**) of the leading EOF of summer (June-September) sea levels in the Caribbean for raw (**a,b**) and detrended (**c,d**) altimetry data. Period of analysis is 1993–2019.  
correlates significantly with Carib SST (+0.45) and the two wind indices (+0.43 and +0.53 with CLLJ and Jamaica wind, respectively). The linear trend is indicative of basin-wide increases in summer sea levels in the long-term which, as noted previously, coincides with a similar long-term warming in Caribbean SSTs. The implication for increasing risk under continued global warming during the time of the year (summer) when climatologically sea level risk is highest is noted. This is discussed further in the final section. In contrast, the timeseries for the detrended data does not significantly correlate with Carib SST.  
The spatial pattern for the detrended data (Figure 5c) shows similarly signed loadings over most of the Caribbean basin, except for just north of South America. Highest loadings are in the north Caribbean. There is a significant correlation with SLP (+0.58), highlighting the role of SLP in driving seasonal sea level variability in the Caribbean basin, also suggested by [21]. Caribbean summer sea level pressures are associated with a southward jog in the North Atlantic Subtropical High [77; 78], which modulates trade wind strengths [68; 79]. The significant and robust correlations with the CLLJ (\(-0.54\)) and Jamaica summer wind (\(-0.68\)) indices are consistent with this.  
Interestingly, there are oppositely signed maxima in the southwestern Caribbean between the location of the CLLJ (around \(15^{\circ}\) N, \(76^{\circ}\) W) and immediately south in the vicinity of the Colombia-Panama Gyre and the Panama Colombia Current. An explanation could be that the SST gradient between the tropical Atlantic and equatorial Pacific influences not only the strength of the CLLJ [55], but also the veering of the winds in its exit region, either northward toward the Gulf (warm Atlantic) or southward toward the Pacific (warm Pacific) [80]. Veering north could influence the strength of the counter flow in the Panama-Colombia Gyre. The SumPC1_detrended timeseries correlates significantly with Pac-Atl (\(-0.50\)) index, Nino3.4 (\(-0.39\)), and the PDO (\(-0.51\)).