FORECAST DISCUSSION

SATURDAY 23rdMAY 2026 AM SHIFT

TODAY:

A southeasterly wind flow continues to prevail across Samoa, while a weak convergence zone lies just north of the group. The morning radiosonde ascent from Pago (22/12Z) indicates sufficient convective potential energy and low-level moisture to support convective development should a lifting mechanism become established, particularly during the afternoon when maximum surface heating and orographic influences are expected to enhance instability. MIMIC Total Precipitable Water (TPW) imagery reveals marginal moisture advection across the group, with precipitable water values around 50 mm. In addition, upper data depict a weak vorticity environment over the forecast area, alongside strong deep-layer wind shear and negative vorticity fields, suggesting that convective cloud development today will be predominantly diurnally driven. For today, expect cloudy periods with brief showers and a few thunderstorms likely in the afternoon.

OUTLOOK: SUNDAY THROUGH THURSDAY

Global weather models suggest that the southeasterly winds will remain dominant through at least Sunday as a high-pressure ridge extends from the south, keeping fair weather conditions over the group. A convergence zone is forecast to establish to the north of Samoa by Monday and may move over the group on Tuesday with the potential for heavy downpours. The weather system is expected to linger over the group through at least Thursday, with a low-pressure system passing across Tonga over the week. In addition, an upper trough is forecast to pass just south of the group from Tuesday, and is likely to enhance convective storm growth and development during this period. Therefore, severe weather conditions are expected during the new week, with the likelihood of a severe weather information issuance before the system’s arrival.

MARINE OUTLOOK:

The latest marine observations from Aunu’u and King-Poloa wave buoys indicate that wave heights are fluctuating below the advisory threshold of 2.5 metres. Global wave models suggest that wave activities may occasionally exceed 2.5 metres, particularly across the southern marine waters during the weekend due to a southerly swell event.

ADVISORIES AND WARNINGS:

NONE

Weather Duty Team:

F. Kalapani, I. Tuatipi, P. Huch & U. Namulau’ulu.