{"id":305,"date":"2026-05-18T23:41:09","date_gmt":"2026-05-18T15:41:09","guid":{"rendered":"https:\/\/pft-s.com.tw\/?page_id=305"},"modified":"2026-05-18T23:41:09","modified_gmt":"2026-05-18T15:41:09","slug":"sample-case-2-taiwan-strait-screening","status":"publish","type":"page","link":"https:\/\/pft-s.com.tw\/en\/metocean-data-service\/sample-case-2-taiwan-strait-screening\/","title":{"rendered":"Sample Case 2 \u2014 Taiwan Strait Site Screening Study"},"content":{"rendered":"

Early-stage metocean comparison across three sites along the Taiwan Strait<\/p>

\u23f1 ~6 min read<\/span><\/p>

This page summarises a methodology sample produced by PF Tech Services Ltd. Full PDF download at the bottom of this page.<\/p>\n\n\n\n\n

\"Over the 2019\u20132023 analysis window, the three sites show distinct characteristics across wind, wave, operability, and typhoon exposure \u2014 no single site is best across all four; a clear three-way trade-off.\"<\/h3>\n\n\n\n\n

Site location<\/h3>

Three sites: North (25.00\u00b0N, 120.44\u00b0E), Mid (24.05\u00b0N, 119.80\u00b0E), South (23.00\u00b0N, 119.57\u00b0E) \u2014 each approximately 50 km from the nearest coastal point of Taiwan.<\/p>\n\n\n\n\n

\u25b6 Executive Summary<\/h2>

At a glance<\/p>\n
Sites<\/td>Three sites along Taiwan's offshore wind development corridor:\u00a0North<\/strong>\u00a0(25.00\u00b0N, 120.44\u00b0E),\u00a0Mid<\/strong>\u00a0(24.05\u00b0N, 119.80\u00b0E),\u00a0South<\/strong>\u00a0(23.00\u00b0N, 119.57\u00b0E). Each site is approximately 50 km from the nearest coastal point of Taiwan.<\/td><\/tr>\n
Window<\/td>2019\u20132023 hourly wind + 3-hourly wave (5 yr)<\/td><\/tr>\n
Sources<\/td>ERA5 single-levels \u00b7 Copernicus Marine WAVERYS reanalysis \u00b7 IBTrACS typhoon catalogue \u00b7 Taiwan Central Weather Administration (CWA) WW3 climatology + CWA buoys (cross-validation)<\/td><\/tr>\n
Distribution<\/td>PUBLIC. \u00a9 2026 PF Tech Services Ltd. Methodology sample, not a project deliverable.<\/td><\/tr>\n<\/table>

Three-way trade-off<\/p>\n\n
Metric<\/th>North<\/th>Mid<\/th>South<\/th><\/tr><\/thead>\n
Annual mean wind10 (m\/s)<\/td>8.91<\/td>8.42<\/td>6.77<\/td><\/tr>\n
Hs p99 (m)<\/td>4.33<\/td>4.66<\/td>3.68<\/td><\/tr>\n
Standard-tier operability (Hs \u2264 2 m AND wind10 \u2264 12 m\/s)<\/td>67%<\/td>68%<\/td>80%<\/td><\/tr>\n
Typhoon passage frequency (within 200 km)<\/td>0.6 \/yr<\/td>1.2 \/yr<\/td>1.6 \/yr<\/td><\/tr>\n<\/tbody><\/table>

The four dimensions show structural differences; no single site is best across all of them.\u00a0North<\/strong>\u00a0ranks highest in mean wind resource and (over 2019\u20132023) has the lowest typhoon passage frequency among the three sites.\u00a0Mid<\/strong>\u00a0\u2014 driven by the mid-strait channel funnelling effect (wind acceleration and directional concentration where the strait narrows) \u2014 has the highest wave extreme value (Hs p99, ~8% above North).\u00a0South<\/strong>\u00a0has the highest operability \u2014 at the standard tier, about 48 more standard operating days per year than the North.<\/p>

5-year absolute extremes (Hs max, wind10 max) and typhoon frequency rankings are event-sample counts over 2019\u20132023, not climatologically stable values; they may not hold under resampling.<\/p>\n\n\n\n\n

What we found<\/h2>

Wave extreme rankings differ from mean wind speed rankings<\/h3>

Annual mean wind speed decreases from north to south (North 8.91, Mid 8.42, South 6.77 m\/s). Annual mean wave height Hs is nearly identical at North (1.60 m) and Mid (1.59 m), with South lower (1.35 m). But at the wave high end (Hs p99), the ranking reverses: Mid 4.66 m, North 4.33 m \u2014 Mid is about 8% higher than North. The cause is the mid-strait channel funnelling effect: the narrowing topography between two coasts accelerates and concentrates winds, occasionally producing larger waves.<\/p>

South has the highest operability, but shows swell-dominated characteristics<\/h3>

South ranks highest across all three operability tiers. The median bad-weather event is shortest (15 h vs North 21 h, Mid 27 h), and the p90 event duration is also shortest (63 h vs North 90 h, Mid 106 h \u2014 i.e. 90% of South's bad-weather events end within 63 h). Annual mean wave height Hs is also lowest at South (1.35 m). \"Bad weather\" here means continuous periods when sea state exceeds operational thresholds and marine operations cannot proceed.<\/p>

However, note that South's time-averaged wave energy is swell-dominated (swell accounts for 47.9% of time-averaged wave energy, exceeding wind-sea at 35.0%), and swell direction differs from local wind direction (swell direction ~138\u00b0, local wind from northeast). This describes the time-averaged energy structure, not the primary driver of extreme events or design loads \u2014 design loads from extreme events are still expected to be wind-sea driven. But period-sensitive operations (lifting, motion-sensitive vessels) at South will be more sensitive to wave period (Tp) variations than at the other two sites \u2014 a nuance not visible from Hs alone.<\/p>

Typhoon exposure varies with latitude \u2014 within this 5-year sample<\/h3>

Over 2019\u20132023, 9 typhoons passed within 200 km of at least one site. Site frequencies: North 0.6\/yr, Mid 1.2\/yr, South 1.6\/yr. North's lower frequency is consistent with Taiwan's terrain providing partial shielding at the strait's north exit; South has the highest exposure, with shorter median passage distance.<\/p>

This is a statistical count over the 2019\u20132023 sample, not long-term climatology \u2014 5 years is a sample snapshot, not a multi-decadal extreme-value estimate.<\/p>\n\n\n\n\n

How we know<\/h2>

Mid-strait channel funnelling signature<\/h3>

Paired wind + wave roses at the three sites (2019\u20132023). Top row: ERA5 10 m wind direction (blue tones); bottom row: WAVERYS total wave direction (orange tones). All three sites show NNE-dominant winds; Mid has the highest directional concentration in the NNE sector \u2014 i.e. channel-funnelling-dominated winds, which in turn drive the wave extreme characteristic.<\/p>

Typhoon tracks within 200 km of the three sites<\/h3>

The nine typhoons (IBTrACS catalogue) that passed within 200 km of any study site during 2019\u20132023. Track colour represents intensity at that point (Saffir-Simpson scale). Numbered labels are placed at each track's first entry point into the map, corresponding to the typhoon event list at the bottom. The three sites are marked with stars, with same-colour dashed circles outlining the 200 km filter range.<\/p>

Operability persistence<\/h3>

Survival curves of operability persistence at the three sites (2019\u20132023). One panel per site, showing curves for three threshold tiers: sensitive, standard, robust. Log scale. The South curve extends further right at the top end (more long-duration operability windows); Mid has the longest single-event tail across all three tiers (a 2,535-hour outlier event in mid-2022, which does not change the median and p90 comparison).<\/p>

Cross-validation against alternative-source 10-year wave hindcast<\/h3>

Monthly mean Hs cross-validation at the three sites: WAVERYS reanalysis (2019\u20132023, orange) vs Taiwan CWA WW3 climatology (2008\u20132017, blue), bilinearly interpolated to each site coordinate. Pearson correlation of the monthly seasonal cycle: North and Mid \u2265 0.97, South = 0.77, supporting the WAVERYS site climatology at the monthly seasonal-pattern level. This validation does not extend to absolute-magnitude verification \u2014 a ~0.25 m systematic bias exists between the three sites, which is non-negligible \u2014 nor does it constitute extreme-value validation.<\/p>\n\n\n\n\n

\u24d8 How to read this sample<\/h2>

This is a\u00a0methodology sample, not a project deliverable<\/strong>. Intended for prospective customers evaluating PF Tech's \"Early-stage Metocean Desktop Study (Level 1 Metocean Desktop Study)\" service:<\/p>\n