SYNOPTIC DISCUSSION

SATURDAY 25th APRIL 2025 AM SHIFT.

TODAY:

An intense high-pressure system centred east of New Zealand continues to direct moderate southeasterly winds, becoming fresh at times across the Samoan group. This weather pattern advect cool and dry wind flow over the region where the available moisture lies at 40-50mm as per MIMIC TPW data. The water vapour satellite imageries also signify drier airmass at the uppers as a high pressure predominates, directing southeasterly aloft. The weak winds from mid levels through the uppers lead to a weak shear environment over the region. In addition, the aforementioned high-pressure system continues to keep a trough of low-pressure with associated convections to the north. But for today, orographic lifting may trigger cloud developments mostly over highlands in the afternoon, although clouds will not be convective as they will be greatly suppressed jointly with drier conditions. Thus, light showers may be observed in some areas, otherwise mostly fine.

SUNDAY THROUGH FRIDAY:

Global weather models suggest the predominance of the cool and dry deepening southeasterly winds throughout this outlook period, due to the intense high-pressure system centred east of New Zealand. However, an upper troughs are forecast to develop over Samoa by Monday and Wednesday, where the axis and upstream predominates the group. The system may aid the development and growth of afternoon thunderstorms, particularly over highlands, although mostly fine weather may be observed in most areas. Therefore, weather models suggest minimal showery activities throughout this outlook period.

MARINE OUTLOOK:

The latest marine observations indicate wave heights ranging well below the advisory threshold of 2.5 metres. However, predictions indicate the progression of a southerly wave surge that will likely elevate wave heights above 2.5 metres over Samoa’s marine waters by mid night Sunday or early Monday. This swell event may coincide with the highest tide of the year expected on Tuesday 28 April 2025, thus the likelihood of a marine advisory may be enforced mainly for southern marine waters.

ADVISORIES/WARNINGS:

NONE

Weather On-Duty Team:

F. Kalapani, A. Sofeni & N. Tutasi.