FORECAST DISCUSSION

TUESDAY 26th MAY 2026 AM SHIFT

TODAY INTO TONIGHT:

A convergence zone remains within the vicinity, which maintains cloudy and moist conditions. Atmospherically, it is considered unstable where both the sounding profile and total precipitable water channel, collaboratively depicted abundant moisture content, weak low-level wind shear, with weak steering winds and moderate instability. In addition, the CIMMS data, revealed negative vorticity field in the 850 hpa, that correlates to the lower level convergence contours over the area, which promoting cloud formation. However, interestingly in the upper atmosphere where regardless of the present strong wind shear, that causes overshooting cloud tops across the country. There’s a upper diffluence due to the eastward movement of an upper trough of low pressure, that generate upper divergence aloft which sustain the surface system’s severity and longevity. Because of that, this pose a high risk of flooding, which impacts major rivers and vulnerable locations. On that note, this issued and enforced the heavy rain warning in all land areas along with the flood advisory for major rivers and vulnerable areas. The model consensus, basically evince that this severe system may persist through tonight followed with the upper divergence aloft lingering over the island chain, which gives a low-to-moderate chance of an upgrade for the flood advisory into the warning category.

OUTLOOK: WEDNESDAY THROUGH MONDAY

According to the weather model guidance, generally suggested that the convergence zone or SPCZ is persisted until Thursday, as it migrated to the north of the forecast area. Simultaneously, the upper trough of low pressure is expected to relocated over Samoa on Wednesday into Thursday, which would further enhanced activities. But, because of an intensified area of high pressure over New Zealand, which will become the dominate weather feature on Friday through Monday in the new week, will direct east-to-southeast winds which hints improving weather, expect trade wind showers and afternoon convections primarily driven through localized effects and diurnal atmospheric patterns. 

MARINE OUTLOOK:

The latest marine observations continue to indicate that wave heights are fluctuating below the advisory threshold of 2.5 metres across Samoa’s marine waters. Global wave models suggest that these wave activities may occasionally exceed 2.5 metres, particularly across the southern marine waters throughout this outlook period, with a low possibility of significant impacts for the mariners.

ADVISORIES AND WARNINGS:

VALID: HEAVY RAIN WARNING @ (11:30 AM)

VALID: FLOOD ADVISORY @ (11:30 AM)

Weather Duty Team:

A. Liu, A. Niko, P. Huch, & S. Maualaivao.