Area Forecast Discussion
Issued by NWS Pago Pago
Issued by NWS Pago Pago
170 FXZS60 NSTU 200037 AFDPPG Area Forecast Discussion National Weather Service Pago Pago AS 137 PM SST Sun May 19 2024 .Short term... Satellite imagery, as of late this morning and early afternoon, shows a mix of sun and clouds over the American Samoa islands as a ridge remains dominant over the region and keeping a trough to the north. A mid-level high to the south of American Samoa will strengthen through the middle of the week to give a change in the weather pattern. From May 1st through this afternoon, WSO Pago Pago recorded 17.98 inches of rainfall. The normal rainfall for the entire month of May is 11.73 inches. The aforementioned mid level high pressure system will finally bring below average rainfall from this evening through the middle of the week. Easterly tradewinds may reach up to 20 mph at times through Monday, then decrease to up to 15 mph through Wednesday. Since much drier air along the lower to mid levels of the atmosphere are expected, this will make it harder for passing showers to develop. If there is a passing shower develops, it will be weak considering a strong inversion is expected at around 3,000 feet (900 mb) by Tuesday and during the day Wednesday. Therefore, the risk of passing showers will decrease from scattered (30-40% chance) to isolated (20% chance) through the middle of the week. There is high confidence that there won`t be a risk of flash flooding through Wednesday. Easterly trades will decrease to around 15 mph, which is well below the Wind Advisory thresholds for American Samoa. .Long term... From Wednesday evening through the rest of the week, we will monitor a potential low pressure system developing near the Fiji region and moving well to the south of the territory. Even though the exact movement of this potential low won`t impact American Samoa from rainfall within that weather system, it would help shift winds to become northeasterly and help drag a trough from the north over the territory. This create conditions that would favor above normal rainfall through the weekend. At this time, any potential rainfall will not be strong enough to create flash flooding over the region. && .Marine... Rough and choppy conditions continue over the American Samoa coastal waters region as fresh to strong easterly trades remain. However, a surface ridge of high pressure that is currently over the region will weaken as it begins to move away from the region tonight. The easterly breeze is expected to become a moderate to fresh breeze for early in the week and becoming an easterly moderate by late in the week. The wind driven conditions are currently the primary reason of the rough and choppy conditions as there are no significant swell anticipated to move through the region for the next 5 days. Therefore, sea heights are forecast to slowly ease throughout the week but is still expected to remain rough through around Tuesday night and Wednesday. The High Surf Advisory remains in effect through Tuesday night. The Small Craft Advisory may be set to expire on Wednesday, but confidence is higher that later in the week would be when conditions will fall below the Small Craft Advisory threshold. && .PPG WATCHES/WARNINGS/ADVISORIES... A High Surf Advisory remains in effect through Tuesday Night. A Small Craft Advisory remains in effect. && $$ LaPlante