Salish Sea Tidal Currents — User Guide

How to view current-atlas pages and build multi-page PDFs for a trip — including a single PDF that shows several subregions at the same time.

The tidal current maps are generated by Richard Dewey in his Salish Sea Tidal Currents Volumes 1–4, freely available at www.dewey.ca. The tidal current maps are based on the tidal model of Foreman et al. (2004). David Leaf, dsleaf@gmail.com, produced the web application that stamps time and date, island names, and CHS and NOAA current-station predictions.

Not for navigation. These charts are planning aids based on a tidal model. Always carry official charts and current tables for navigation decisions.

1. What these apps do

Each app shows the Salish Sea Tidal Current Atlas for one region. You pick a date and hour, and it shows the atlas page for that moment — the arrows on the page show current direction and strength. Every map can be stamped with the exact date/time and live current-station predictions, then exported as a JPEG or PDF you can carry offline on a phone or tablet.

AppRegionSubregions
SJISan Juan Islands (Vol. 1)A–H
DBDiscovery & Broughton IslandsA–H
NGSNorthern Georgia StraitA–H
PSPuget Sound (Vol. 2)A–F

The subregion letters are the tabs across the top of the app. Tap 🗺 … Subregions to see a map of which letter covers which area.

2. Viewing a single map

  1. Choose a Month and Day (it opens on today's date).
  2. Click a subregion tab (A, B, C …) for the area you care about.
  3. In the Hourly Atlas Pages table, click the row for the hour you want. The map appears on the right, stamped with the date/time and any current-station predictions for that moment.

Zoom with the − / + buttons. The stamp you see on screen is exactly what gets burned into your exported files.

3. Build & Export — making a trip PDF

The ⚙ Build & Export button is how you generate a multi-page document in one step. Click it to open the panel, then fill in:

FieldWhat it does
Start / End DateThe day range to cover. Use the same date in both for a single day.
Start / End TimeThe hours of each day to include (e.g. 07:00 to 19:00 for daylight).
SubregionsComma-separated letters, e.g. A,B,C. The order you type them is the order they appear in the PDF.
Page OrderTime-major or Sub-major — see section 4.
Split PDF / N daysBreak a long trip into one PDF per N days. Leave blank for a single PDF.
Phone PDFAlso build a smaller, phone-sized version of the PDF.

As you type, the estimate (e.g. ≈ 48 maps · 2 days · 1 PDF) updates so you know the size before building. Click Build & Export, wait for it to finish, then click the download links that appear (one JPEG ZIP plus one PDF, and a phone PDF if you ticked it). If a split produces several PDFs, a ⬇⬇ All PDFs button downloads them all at once.

4. Showing several subregions at the same time

This is the key choice for trip planning. The Page Order setting decides how the pages are interleaved.

🕐 Time-major recommended for trips

For each hour, it places every subregion you listed back-to-back. Flip through the PDF one hour at a time and see the whole route's currents together.

Sub A — 8 am
Sub B — 8 am
Sub C — 8 am
Sub A — 9 am
Sub B — 9 am
Sub C — 9 am …

🅰 Sub-major

For each subregion, it places every hour in a block. Good when you want all of one area's pages together.

Sub A — 8 am
Sub A — 9 am
Sub A — 10 am …
Sub B — 8 am
Sub B — 9 am …

Example: see currents across your whole route, hour by hour

You're paddling through three subregions on July 18 and want one PDF where each hour shows all three areas side by side as you flip pages.

  1. Start Date & End Date: 2026-07-18 (same day in both).
  2. Start Time 07:00, End Time 18:00.
  3. Subregions: A,B,C (in the order you'll travel them).
  4. Page Order: Time-major.
  5. Click Build & Export, then download the PDF.

The result: A 7am, B 7am, C 7am, A 8am, B 8am, C 8am … — at every hour you see all three subregions together.

Example: watch each area change hour by hour

You want each subregion's pages grouped together so you can follow how that one area's current builds and slackens through the morning.

  1. Start Date & End Date: 2026-07-18 (same day in both).
  2. Start Time 08:00, End Time 11:00.
  3. Subregions: A,B.
  4. Page Order: Sub-major.
  5. Click Build & Export, then download the PDF.

The result: A 8am, A 9am, A 10am, A 11am, B 8am, B 9am … — each area's hours stay together, so you can see how the current in that one subregion changes over the morning.

5. Hand-picking maps for your exact route (manual selection)

Build & Export covers whole date/time blocks. But when your trip threads through several subregions at different times — you're in area A at 8 am, cross into area B by 9 am, reach area C by 10 am — you can pick exactly those maps by hand and export just them, in the order you'll travel.

  1. Pick the date at the top.
  2. Click the subregion tab for the first leg of your route (e.g. A).
  3. In the Hourly Atlas Pages table, tick the checkbox for the hour you'll be there (e.g. 08:00). The selected count goes up.
  4. Switch to the next subregion tab (e.g. B) and tick the hour for that leg (e.g. 09:00). Keep going for each leg — your ticks are remembered as you change tabs.
  5. Click Extract Selected Maps. You get a ZIP of stamped JPEGs plus a PDF, in the order you selected — a page-by-page picture of the currents you'll actually meet along the way.

Use Prev / Next to step through your selected maps on screen, All to select every hour shown for the current subregion, and Clear to start over.

6. Phase Pick — auto-select around a tidal phase

The ⏱ Phase Pick button selects every atlas page that sits closest in time to a chosen tidal phase — Max Flood, Max Ebb, Slack before Flood, or Slack before Ebb — at a reference station, over a date range. It's faster than ticking rows by hand when you only care about the same moment in each tidal cycle.

  1. Click ⏱ Phase Pick to open the panel.
  2. Choose a Reference Station — the tide station whose phases drive the picks.
  3. Choose a Phase: Around Max Flood, Around Max Ebb, Around Slack before Flood, or Around Slack before Ebb.
  4. Set the Start Date and End Date.
  5. Type the Subregions you want covered (e.g. B or A,B,C).
  6. Click Find & Select. Every atlas page closest to the chosen phase, on each day in the range, is ticked in the Hourly Atlas Pages table. From there you can step through them with Prev / Next, or click Extract Selected Maps to export a stamped JPEG/PDF bundle.

Why "Around"? Tide stations predict the exact clock time of Max Flood, Max Ebb, or Slack — but the atlas pages are produced at fixed hourly intervals. The predicted phase rarely lands exactly on a top-of-hour map. Around Max Flood means the atlas page whose time is closest to the predicted peak (usually within 30 minutes), not an exact match.

7. Tips