Ocean Surface Wind Plots

This web applet generates near-real-time ocean surface wind maps over the Western Pacific, primarily over Weather Forecast Office (WFO) Guam's Area of Responsibility (AOR), in the area from 120 to 180°E, between 5°S and 45°N, using satellite scatterometer data provided by the Royal Netherlands Meteorological Institute (KNMI). It renders wind barbs on an interactive map, which then can be exported as publication-quality charts.

Supported Sensors

Sensor	Satellite(s)
ASCAT	Metop-B, Metop-C
OSCAT-3	OceanSat-3
HSCAT	HY-2B, HY-2C, HY-2D**

**Non-Operational since 2024

How to Use

1. Select Sensors

Check one or more sensor boxes at the top of the control bar. ASCAT is selected by default. You may select any combination of ASCAT, OSCAT-3, and HSCAT.

2. Choose a Run

Click one of the run buttons:

Auto: automatically picks AM or PM based on the current time in Chamorro Standard Time (ChST, UTC+10). Between 0800 and 1800 ChST it selects the AM run; otherwise the PM run.
AM: descending satellite passes (2100~0900 UTC).
PM: ascending satellite passes (0900~2100 UTC).

3. Select a Date (Optional)

Click the date field to pick a specific date. If left blank, the tool uses today's date (or yesterday, depending on the run window and current time).

4. Generate the Map

Click Generate Map. The tool will:

Search the KNMI FTP server for available satellite granules in the selected time window.
Download and extract wind data from each granule (cached locally to speed up repeat runs).
Filter observations by pass direction and time window.
Bin wind vectors onto a 0.25° grid.
Render color-coded wind barbs on the interactive map.

The status bar shows progress at each step. You can click Cancel at any time to abort.

5. Toggle Between Sensors

When multiple sensors are selected and produce data, a toggle bar appears below the status bar with a button for each sensor plus an All Combined option. Click any button to switch the displayed map to that sensor's data.

6. Adjust Sensor Weights

Next to each individual sensor button in the toggle bar, a weight slider (0–100%) controls how much that sensor contributes to the Combined view. Adjusting a slider instantly recomputes and redraws the combined map.

Example: Setting ASCAT to 100% and HSCAT to 25% means that in grid cells where both sensors have observations, ASCAT data dominates the averaged wind vector. Setting a sensor to 0% excludes it entirely from the combined view.

7. Toggle Swath Labels

The Labels checkbox (next to the sensor checkboxes) controls whether satellite pass labels are shown on the map. These labels identify each swath strip by satellite name and overpass time. Unchecking the box hides them immediately. Downloads will also omit labels when the box is unchecked.

Downloads

Download View

Exports the current interactive map view exactly as shown, including the visible tile background, wind barbs, overlays, and colorbar. Saved as ascat_winds_view.png at 200% viewport resolution.

Download Chart (300 DPI)

Generates a publication-quality chart covering the full Western Pacific domain (34″×22″ at 300 DPI). The chart includes its own independently loaded map tiles, wind barbs at print scale, grid lines with labelled axes, place labels for key locations across the Marianas and Micronesia, a wind speed colorbar, title, attribution, and watermark.

Filenames follow the pattern:

Active View	Example Filename
ASCAT	`ASCAT_BC_20260329_AM.png`
OSCAT-3	`OSCAT3_20260329_PM.png`
HSCAT	`HSCAT_20260329_AM.png`
All Combined	`MULTI_SENSOR_20260329_PM.png`

What the Map Shows

Wind barbs: Full barbs; 10 knots, half barbs; 5 knots, flags; 50 knots.
Color: Wind speed in knots, using the NOAA/STAR palette.
Swath Labels: Colored badges at the domain edges identifying each satellite pass by name and UTC overpass time. Ascending passes are labelled at the top (45°N); descending passes at the bottom (5°S).
Place Labels: Key locations across the Marianas and Micronesia, including Guam, Saipan, Palau, Yap, Chuuk, Pohnpei, Kosrae, Majuro.
Colorbar: Wind speed legend on the right side of the map.

AM vs PM Runs

AM Run (0800–1800 ChST) collects descending satellite passes from the preceding night through the morning (2100~0900 UTC).
PM Run (1800–0800 ChST) collects ascending satellite passes from the daytime period (0900~2100 UTC).

Each sensor has its own orbital timing, so the exact UTC windows differ slightly. The tool computes sensor-specific windows automatically based on each satellite's Local Time of Descending Node (LTDN).

Data & Attribution

All scatterometer wind data is provided courtesy of the Royal Netherlands Meteorological Institute (KNMI). The wind speed color scale follows the NOAA/STAR palette. Base map tiles are provided by CartoDB (Positron) with OpenStreetMap data.