SYNOPTIC DISCUSSION

FRIDAY 22NDAUGUST 2025 AM SHIFT

TODAY INTO TONIGHT:

The variation in the weather conditions of this morning is due to the remaining persistence of the moderate southeasterly wind flow across our area of responsibility. This is associated with dry and stable conditions with a few showers possible in some areas of the islands. The increase in cloud coverage that was observed this morning is due to the dominance of low-to mid-level clouds, which correlates with the slightly broader area of vorticity at 850 mblevel according to CIMMS observations. The prevalence of the aforementioned wind-flow is expected to prolong in the afternoon with the surface heating and possible slight lifting may enhance some brief precipitation mainly over elevated and windward areas this afternoon. The collections of satellite data, in conjunction with the MIMMC TPW animation, describe the chain area of broad convections which develop to the north of the group, which illustrates the SPCZ system. This system is forecast to approach the forecast zone tonight and may trigger a gradual development of showery activities across the country for tonight.

SATURDAY THROUGH THURSDAY:

Global weather models indicate that a convergence zone advancing from the north is anticipated to make landfall by early Saturday, resulting in widespread showers with the possibility of moderate to heavy falls. This weather system is projected to move entirely south of the group by Saturday evening, enabling the surface easterly winds to commence. The easterly trade winds are expected to prevail until Monday, after which they will transition to a northeasterly direction by Tuesday. Speed convergence along the easterly wind flow may lead to sporadic showers across the group on Monday. At mid-levels, northeasterly steering winds are expected to emerge from Saturday, with a high-pressure ridge anticipated to form over the region by the beginning of the new week. Furthermore, the absence of significant upper-level forcing over the forecast area during this outlook period implies that cloud formation will primarily be driven by diurnal cycles, with minimal enhancement of vertical motion. Nevertheless, model predictions suggest the possible emergence of a region of upper diffluence just northwest of the islands on Saturday, which could offer favorable dynamical support for deep convection and likely assist in the intensification of the related surface system.

MARINE OUTLOOK:

The latest compilation of marine observational data indicates that wave and swell heights are below the advisory threshold of 2.5 meters. This trend in wave activity is expected to persist during the forecast period. Consequently, there is no immediate threat to Samoa's coastal and marine waters.

ADVISORIES/WARNINGS:

NONE

Weather Duty Team:
Gospel. N, Lao. Ioane. T, Samuelu. T & Andrew. S