A large, long-period northerly swell is staring to make its way into the region, reaching the northern Marshall Islands tonight and Majuro by Friday. These waves were generated by a strong north Pacific cyclone currently about 2750mi northeast of Wake Island. Wave model guidance shows 7-11 foot northerly swell with periods of 14-17 seconds around the peak of this event Friday - also well timed with the full moon phase and its higher high tides. Drifting buoys through the region overall support model guidance leading to high confidence in the strength of the swell. All this still supports the development of hazardous to dangerous surf and hazardous marine conditions for small craft. Additionally for islands and atolls well exposed to the north, there will be the increased threat for significant erosion and some minor inundation. Today's PacIOOS wave run-up guidance for Majuro still shows the potential for minor inundation around high tides. While more southern atolls could see some shadowing from atolls farther north, the degree of shadowing is uncertain and the northernmost atolls will see the largest and unimpeded swells. For the northern islands, dangerous surf around 15 feet is likely, with the greatest risk for coastal inundation along north facing shores exposed to the open ocean, and also within the lagoons. Water can pile into lagoons if open to the ocean on their north side and closed along the southern edge with few reef passes to allow water to flow through. This can cause debris to cover vulnerable property, roads and even airport runways. Sea heights will be around 12 to 14 feet, making inter-travel between island hazardous until the north swell starts to drop Saturday. Atolls such as Majuro, Kwajalein, Jaluit, and Mili, may be shadowed by the more northern islands, potentially reducing the max surf and sea height, but how much shadowing the atolls will experience is uncertain. Current model guidance supports surf up to 11 feet at Majuro with seas around 9 feet, just under hazardous levels for surf and small craft respectively. Minor coastal inundation is still possible, with the greatest risk along north facing shores exposed to the open ocean and within the lagoons. Residents should monitor local sea conditions and forecasts and be alert for minor flooding and debris on roads and property near shore lines, along with dangerous surf, swimming, and boating conditions. Stay up to date with information from your Weather Service Office in Majuro, and any information shared from local emergency management offices. The latest Majuro forecasts can be found at weather.gov/gum/PublicForecasts.
