The Central Weather Administration extended astronomical high-tide advisories through Tuesday for Penghu County and Changhua’s western lowlands as overlapping spring tides and residual swell from Typhoon Shuleki pushed seawater against levees. Farmers in coastal townships reported brief saltwater intrusion into drainage canals, though no major breaches were recorded overnight.
Science behind the advisory
Astronomical tides peak when lunar and solar gravity align near the autumn equinox, adding 30 to 40 centimeters to baseline levels even without storm surge. Shuleki’s passage to the north left long-period waves that continued to stack on top of those peaks along Taiwan’s west coast. CWA modelers said the combined effect would ease after the September 30 high-tide window if winds stay light.
Penghu’s island geography leaves few outlets when harbor mouths face sustained onshore flow. County crews placed portable pumps near vegetable greenhouses in Huxi and Xiyu townships and asked oyster farmers to raise racks one rail higher than usual.
Changhua flood gates
In Changhua, irrigation associations closed flood gates linking paddy fields to the Taiwan Strait during the highest tide bands, then reopened them during outgoing flow to flush salt. The procedure is routine but labor-intensive, and volunteers were scarce during the Mid-Autumn holiday.
Climate context
Sea-level rise has amplified historical tide tables used by Taiwanese engineers. CWA updates now include satellite altimetry adjustments that were not in legacy levee design manuals from the 1990s. Coastal legislators used the advisory to argue for faster dredging budgets in next year’s disaster-prevention bill.
Public safety
Tourists visiting Penghu’s intertidal zones were asked to avoid night photography on wet basalt platforms when waves overlap high tide. Mainland Taiwan ferry operators maintained schedules but warned of rolling delays if berth approaches flood.
Outlook
Forecasters expect Shuleki’s swell to decay by midweek, leaving only astronomical factors. Until the advisory expires, lowland residents should monitor county text alerts and keep drainage ditches clear of holiday debris.
Engineering follow-up
Water Resources Agency crews will survey levee toe erosion in Changhua after the advisory ends, feeding data into next year coastal reinforcement budget requests debated in the new legislative session.