FORECAST DISCUSSION

THURSDAY 7THMAY 2026 PM SHIFT

TONIGHT:

A low-pressure system centred southeast of Tonga extends its associated convergence zone just southeast of the Samoa. The position of the col area near the north of Samoa contributes in weak convection over the group, where mostly cloud-free conditions persist during the day as per satellite data. Water vapour satellite imagery reveals dry airmass advection at mid and upper level atmosphere as polar southwesterly aloft continues to persist. The afternoon ascent from Pago (07/00z) reflects dry vertical profile at mid to upper levels with strong atmospheric instability and a deepening northerlies maintaining the moist wind flow. MIMIC Total Precipitable Water (TPW) imagery reveals moisture advection over the region where values exceed 50mm. In addition, upper data indicate a weak vorticity environment over the forecast area along with a strong deep-layer shear, suggesting short-lived convection if triggered heading into the night. For tonight, fine weather is expected apart from some brief showers and a chance of few thunderstorms.

FRIDAY THROUGH WEDNESDAY:

Global weather models suggest that the low-pressure system centred further south will continue moving southward, dragging major rain bands away from the group. However, a high-pressure system is forecast to develop southwest of Fiji, directing southeasterly winds that may converge with easterly trade winds over Samoa on Saturday, bringing showery conditions across the group. From Sunday through Monday, moderate southeasterly winds are forecast to dominate the surface, veering to gentle easterly flow from Tuesday, with mostly fine weather conditions during this period. Localized afternoon convection is possible over highland areas during this outlook. In addition, a mid-level ridge of high pressure may dominate the forecast area during this outlook forecast, while strong westerly to southwesterly flow persists at the uppers. The lack of significant upper lifting over the region suggests that cloud development will be largely diurnally driven.

MARINE OUTLOOK:

The latest marine observations from Aunu’u and King Poloa wave buoys as well as altimeter data indicate that wave heights have fluctuatedaround 2 metres over the past 12 hours. Global wave models suggest that wave activities will continue to fluctuate below the advisory threshold of 2.5 metres during this outlook period.

ADVISORIES/WARNINGS:

NONE

Weather Duty Team:

F. Kalapani, S. Kalolo, L.I. Tuatipi & N. Tutasi.