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Area Forecast Discussion
Issued by NWS Pago Pago
Issued by NWS Pago Pago
003 FXZS60 NSTU 200128 AFDPPG Area Forecast Discussion National Weather Service Pago Pago AS 228 PM SST Fri Jul 19 2024 .Short term... Satellite imagery shows only very few clouds over the American Samoa islands. The last few balloon launches from WSO Pago Pago has shown a very strong inversion around 3,500 above the surface. This indicates a warming trend at that level, which creates conditions that are difficult for clouds to develop. If a few clouds are able to develop, these cumulus clouds are much thinner than normal and are very unlikely to produce rainfall. We expect this type of weather pattern to continue through at least Saturday night. The weather pattern shifts as the high pressure system moves eastward by Sunday morning. A strong inversion remains, but that warming trend will not occur until higher up in the atmosphere (to around 5,500 feet). If clouds develop, the clouds will be slightly thicker and will increase the risk of a passing shower to around 10% chance (for the rest of the day through Saturday night) to around 30% chance of a passing showers (from Sunday night through Tuesday night). If showers develop, the confidence is very high that the rainfall will not produce flash flooding over the region. Easterly tradewinds are anticipated to increase throughout the weekend and early next week due to a trough to the north interacting to the ridge over the islands. Expect trades to increase to eventually reach up to 25 mph by Sunday and to remain around that strength through at least Wednesday morning. At this time, the wind strength is below Wind Advisory threshold levels. However, we will continue to monitor wind speeds throughout the weekend. .Long term... The dry weather pattern through the middle of the week is expected to end by late week. The aforementioned ridge will move away from the region and will bring the trough, currently well to the north of American Samoa, south to move over the islands by as early as Wednesday evening. Numerous showers are likely late in the week and will monitor if there is a possibility of flooding with these showers throughout the week. As the trough moves over the region, the easterly trades will become northerly. && .Marine... The latest information from the PacIOOS buoys located to the east and west of Aunu`u shows ideal conditions, especially for this time of the year, along the American Samoa coastal waters. The easterly trades decreased to around 10 knots throughout the day and only mixing with weak southerly swell. However, easterly trades will increase throughout the weekend to eventually reach to around 20 knots by Sunday. This will cause seas to slowly build throughout the day on Saturday to eventually reach 9 to 12 feet by Sunday and is expected to remain through the middle of the week. Even though long period swell is forecast to finish moving through the coastal waters by Sunday, the wind driven waves are expected to create choppy and hazardous conditions from Sunday through the middle of the week. && .PPG WATCHES/WARNINGS/ADVISORIES... NONE && $$ LaPlante