FORECAST DISCUSSION

WEDNESDAY 20thMAY 2026 PM SHIFT

TONIGHT INTO TOMORROW:

A light and variable winds remain prevalent over the vicinity, with associated clouds and showery activities impacting the area of responsibility. A collection of satellite data, indicated developing convective clouds as low-level moisture content continue to persist, present dry slot and instability. In addition, CIMMS observations depicted lower level convergence, that clarifies vertical cloud growth, signifying a weak trough slightly to the south, regardless of the strong wind shear and upper convergence, hindering activities to the surface. As for tomorrow, model consensus forecasted that the weak trough to south drifted to the south, where a ridge of high pressure extending from the south, causing the wind flow to be southeasterlies. Thus, anticipate afternoon showery and thundery activities mainly over highlands.  

OUTLOOK: SATURDAY THROUGH WEDNESDAY

Numerical weather models, generally forecasted that throughout the outlook period as the previously stated ridge of high pressure which will maintain trade wind regime, providing showers along the mean wind flow, with diurnal weather patterns primarily elevated windward areas. However, a convergence zone moving from the southwest linked to developed low circulation located northwest of New Zealand, where a low probability of generating accumulated rainfall activities on Tuesday into Wednesday. At the mid-levels, a high-pressure area may linger to the north of Samoa throughout this outlook period, directing westerly steering flow across the group. Strong westerly winds are forecast to persist at the uppers throughout this outlook, and with the absence of a significant upper-level forcing, cloud development will be largely diurnally driven. Therefore, mostly fine weather conditions are expected across Samoa during this outlook period, apart from localized convective cells.

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 will remain below 2.5 metres through at least Saturday, before a southerly swell enters the southern marine waters of Samoa with a low probability of exceeding the advisory threshold.

ADVISORIES AND WARNINGS:

NONE

Weather Duty Team:

A. Liu, S. Kalolo, P. Huch, &  N. Tutasi.