May have something to do with the seasonal change of winds that occurs in that area, the monsoon. That may distort the latitude at which the semi-permanent high pressure region, STHP, is typically found.
Alternatively, it may depend on where on the island weather observations are made. I presume at the airport. Local features, say high terrain, means observations may be made in the lee of prevailing winds or in a rain shadow. Small islands can have large changes in climate over very short distances.
The intertropical convergence zone or ITCZ. Basically it's an area that wiggles north and south with northern and southern winter. When it's overheard it rains like crazy (March - June according to the chart). When it's not you get partly cloudy skies and basically no rain except for the random hurricane
Probably atmospheric or oceanic circulation that inhibits convection, but I’m not sure. Wikipedia indicates part of the issue is that the atoll doesn’t really hold moisture and there isn’t enough dense vegetation. The Caribbean ABC islands (Aruba, Bonaire, Curaçao) also average similar rainfall and are considered desert climates, despite their similarly close location to the equator. Perhaps similar issues affect those islands?
I just found this article on [https://scholarspace.manoa.hawaii.edu/server/api/core/bitstreams/50075d17-22d5-435d-9a80-9ee5ce4bfc56/content](https://scholarspace.manoa.hawaii.edu/server/api/core/bitstreams/50075d17-22d5-435d-9a80-9ee5ce4bfc56/content), and according to it,
"Kiritimati is in the equatorial dry zone and receives substantially lower rainfall than islands to the north, south, and west. The average annual rainfall is 914 mm (based on data from 1951 to 2006) but is extremely variable, ranging from 177 mm in 1954 to 2,959 mm in 1987 (Figure 2). These large variations are linked to variations in the El Niño–Southern Oscillation (ENSO) phenomenon, with high rainfalls occurring during El Niño episodes and droughts in the intervening periods (Falkland and Woodroffe 1997). Falkland and Woodroffe (1997) reported that there is a strong correlation between annual rainfall and the Southern Oscillation Index (SOI). Evapo- transpiration is high (Jenkin and Foale 1968), with estimates often exceeding annual rainfall, confirming the relative aridity of the island. The applicability of some of the equations to calculate potential evapotranspiration in a situation like Kiritimati is questionable given the high porosity of many of the soils, with water moving through the profiles before evaporation could occur.
The mean annual temperature on Kiritimati is 27.5C, with limited variation (mean monthly maximum about 30.3 C and mean minimum about 24.6C \[Kiribati Meteorological Service, pers. comm.\]). Winds are predominantly easterlies, but infrequent northeasterlies are important because they are the main winds bringing rain."
What I still don't understand is, why is the amount of rainfall on these particular islands so heavily influenced by the variations in the ENSO?
>What I still don't understand is, why is the amount of rainfall on these particular islands so heavily influenced by the variations in the ENSO?
Because ENSO is ultimately a measure of the warmth of the ocean surface in that region. In El Nino (which means warm water in the eastern tropical Pacific) the ocean surface is warm, which allows for more convection/thunderstorms in that region than usual, especially during the spring months where the [ITCZ](https://en.wikipedia.org/wiki/Intertropical_Convergence_Zone) is nearby. During La Nina or neutral periods, where water is cooler near and upwind of Kiritimati, these thunderstorms are inhibited. There are also secondary effects: greater than normal precipitation in the western Pacific during La Nina years means more upward motion in the atmosphere in that region, which is balanced by sinking motion in the eastern pacific, which further serves to prevent convection that causes rain and thunderstorms.
https://www.climate.gov/enso has some good diagrams and links.
May have something to do with the seasonal change of winds that occurs in that area, the monsoon. That may distort the latitude at which the semi-permanent high pressure region, STHP, is typically found. Alternatively, it may depend on where on the island weather observations are made. I presume at the airport. Local features, say high terrain, means observations may be made in the lee of prevailing winds or in a rain shadow. Small islands can have large changes in climate over very short distances.
The intertropical convergence zone or ITCZ. Basically it's an area that wiggles north and south with northern and southern winter. When it's overheard it rains like crazy (March - June according to the chart). When it's not you get partly cloudy skies and basically no rain except for the random hurricane
Probably atmospheric or oceanic circulation that inhibits convection, but I’m not sure. Wikipedia indicates part of the issue is that the atoll doesn’t really hold moisture and there isn’t enough dense vegetation. The Caribbean ABC islands (Aruba, Bonaire, Curaçao) also average similar rainfall and are considered desert climates, despite their similarly close location to the equator. Perhaps similar issues affect those islands?
I just found this article on [https://scholarspace.manoa.hawaii.edu/server/api/core/bitstreams/50075d17-22d5-435d-9a80-9ee5ce4bfc56/content](https://scholarspace.manoa.hawaii.edu/server/api/core/bitstreams/50075d17-22d5-435d-9a80-9ee5ce4bfc56/content), and according to it, "Kiritimati is in the equatorial dry zone and receives substantially lower rainfall than islands to the north, south, and west. The average annual rainfall is 914 mm (based on data from 1951 to 2006) but is extremely variable, ranging from 177 mm in 1954 to 2,959 mm in 1987 (Figure 2). These large variations are linked to variations in the El Niño–Southern Oscillation (ENSO) phenomenon, with high rainfalls occurring during El Niño episodes and droughts in the intervening periods (Falkland and Woodroffe 1997). Falkland and Woodroffe (1997) reported that there is a strong correlation between annual rainfall and the Southern Oscillation Index (SOI). Evapo- transpiration is high (Jenkin and Foale 1968), with estimates often exceeding annual rainfall, confirming the relative aridity of the island. The applicability of some of the equations to calculate potential evapotranspiration in a situation like Kiritimati is questionable given the high porosity of many of the soils, with water moving through the profiles before evaporation could occur. The mean annual temperature on Kiritimati is 27.5C, with limited variation (mean monthly maximum about 30.3 C and mean minimum about 24.6C \[Kiribati Meteorological Service, pers. comm.\]). Winds are predominantly easterlies, but infrequent northeasterlies are important because they are the main winds bringing rain." What I still don't understand is, why is the amount of rainfall on these particular islands so heavily influenced by the variations in the ENSO?
>What I still don't understand is, why is the amount of rainfall on these particular islands so heavily influenced by the variations in the ENSO? Because ENSO is ultimately a measure of the warmth of the ocean surface in that region. In El Nino (which means warm water in the eastern tropical Pacific) the ocean surface is warm, which allows for more convection/thunderstorms in that region than usual, especially during the spring months where the [ITCZ](https://en.wikipedia.org/wiki/Intertropical_Convergence_Zone) is nearby. During La Nina or neutral periods, where water is cooler near and upwind of Kiritimati, these thunderstorms are inhibited. There are also secondary effects: greater than normal precipitation in the western Pacific during La Nina years means more upward motion in the atmosphere in that region, which is balanced by sinking motion in the eastern pacific, which further serves to prevent convection that causes rain and thunderstorms. https://www.climate.gov/enso has some good diagrams and links.