[Diving with Datou] 3 Steps to Reading the Windy App — Master Dive Conditions on Your Own

"Hey instructor, can we dive Chaojing tomorrow?" / "Boss, the wave height looks like 1.5 m tomorrow — does that mean Chaojing is out?"

After earning his dive instructor certification, Datou has been busy teaching and guiding Fun Dive guests who come specifically to dive Chaojing. These two questions come in almost every evening before an outing. Bad weather always puts a damper on diving, but when a diver who's been cooped up for too long finally gets a day off, missing out on a dive is absolutely gutting. So this time, Datou is sharing a simple 3-step method for deciding whether conditions are good enough to dive.

Step 1: Identify Your Dive Area

Obvious, right? You'd already know where you're going before you even start planning! Hold on — what we're talking about here is the concept of area, because the local topography directly affects whether diving is suitable.

Take Green Island as an example. The water temperature there is comfortable year-round, making it suitable for diving in all seasons — yet dive shops still choose their sites based on which direction the monsoon is blowing. In winter, when the northeast monsoon kicks in, the northeastern side of the island becomes unsuitable for diving. Conversely, when the southwest airflow strengthens in summer, dive shops try to avoid the southwestern side of Green Island.

That said, this is still a broad generalisation. Let's get more specific and use Wanghaixiang Bay (Chaojing Marine Park) — Datou's home turf — as our example. The diving season there runs roughly from May to September each year. An easy way to remember it: after the Dragon Boat Festival and before the Mid-Autumn Festival. Both water temperature and wave conditions tend to be most diver-friendly during that window.

Once you know your general dive area, you can move on to selecting specific dive sites.

Step 2: Combine Topography + Windy App to Evaluate Sites and Entry/Exit Points

Let's dig into the details using Datou's home ground. First, establish a key reference point: Wanghaixiang Bay faces northeast.

Next, please download the Windy App.

• iOS version

• Android version

If you're searching for it, note that there are 2 Windy apps in the store — make sure you download the blue one on the right!

Once you've downloaded Windy, select your location by searching for Taiwan-潮境公園. After tapping in, you'll see a timeline of various conditions. The three readings divers need to pay the most attention to are:

• Swell, m

• Swell size, m

• Swell period, s

Swell size, m: Wave Height

As a general rule, if wave height exceeds 1 m, diving is not recommended. On a boat dive, swells can cause rough, uncomfortable surface conditions; for shore dives, large waves make entry and exit difficult and risky, and waiting on the surface leaves divers prone to seasickness. That said, it's never that simple — if every shop shut down whenever waves exceeded 1 m, the Northeast Coast would barely have any business days at all!

Swell, m: Swell Direction

The devil is in the details! Remember how we said Wanghaixiang Bay faces northeast? That means when the northeast monsoon is blowing, swells from the northeast build enormous energy and slam straight into the exposed face of the bay — making it unsuitable for diving. Yet just across from Chaojing, sites like Shen'ao and Crystal Palace may be sheltered enough to still allow diving.

Flip the scenario to summer: as the southwest airflow strengthens, certain dive sites at Kenting and Xiaoliuqiu may become impossible to enter — while Wanghaixiang Bay, sitting on the sheltered side, can be as flat as a lake.

For instance, at the time of writing (2019/7/3), checking Windy for that Saturday showed a seemingly alarming wave height of 1.6 m — but because the swell was coming entirely from the south, conditions that day were actually very suitable for diving! (Forecasts are for reference only; always assess actual on-site conditions.)

There's also the finer detail of choosing your entry and exit points. Anyone who's dived Wanghaixiang Bay knows the usual entry point is next to a metal frame structure, using a giant-stride entry, while the typical exit is through a channel adjacent to that same frame — fins off first, then walk ashore. That channel runs in a southeast direction. If the swell is coming from the southeast, powerful wave energy funnels straight in, surging back and forth through the channel — extremely dangerous for divers hauling heavy gear in and out of the water. We've also seen plenty of freedivers get pushed into the rocks and come up with cuts and bruises.

Conversely, the other entry point at the fishing reef channel faces directly northeast. On days with a northeast swell, we generally avoid using that entry/exit point.

Swell period, s: Wave Period

If you cast your mind back to your Open Water course, you'll recall that the wave period is the distance between two successive wave crests. Most waves are driven by wind and affect only the surface layer — but when a powerful typhoon pushes energy from the open ocean toward shore over a long distance, it generates long-period swells, commonly called groundswells. Marine scientists generally define a groundswell as having a period of 10 seconds or more. Taiwan's Central Weather Bureau defines it as waves exceeding 1.5 m with a mean wave period over 8 seconds, and will issue public advisories accordingly.

Groundswells carry significant energy and affect greater depths. Underwater, divers can feel a pronounced back-and-forth surge caused by the waves. If you've just entered the water, swim deeper to reduce the effect. If you're heading back to shore and can't avoid the surge, stop kicking your fins when the swell pulls you backward, then kick hard when the next wave pushes you forward — this lets you use the surge to your advantage. When moving between reef formations, be careful not to be slammed into the rocks by the surge.

Putting your fins on and taking them off efficiently is critical — never linger in the surf zone struggling with your fins. Make it a habit; practise quick fin changes during entry and exit.

Step 3: Choose the Best Time to Enter the Water

Once you've selected your dive area and site, everyone wants to know when the current will be at its weakest and the visibility at its best. Time to dust off your Open Water course notes again.

The 1st and 15th days of each lunar month bring spring tides — larger tidal ranges mean more water moving in and out of any given space in the same amount of time, which naturally produces stronger currents. If your schedule allows, try to plan your dives around neap tide days instead!

Within each day, there are roughly two high tides and two low tides. Experience shows that at the turn of the tide — when it's at its fullest high or lowest low — currents are at their weakest and visibility tends to be at its best. The first incoming tide of the day usually stirs up suspended particles from the depths, so visibility after the initial flood tide is often poor.

Finally, at Wanghaixiang Bay, the incoming tide flows in from the northern mouth of the bay — so when diving inside the marine reserve during a flood tide, the current will push you inward. On the ebb, it will carry you outward. Use this information to plan your dive: figure out in advance whether you'll be swimming with or against the current. For example, during a spring flood tide, we'll usually enter at the fishing reef and drift back to exit by the metal frame.

The insights above are drawn from our accumulated experience diving at Wanghaixiang Bay. They broadly apply to other dive sites too — but every location has its own unique hydrology and topography. If you're unfamiliar with a site, we strongly recommend hiring a local dive guide so you can enjoy yourself safely! (We've heard from experienced divers about sites where the surface current runs completely opposite to the bottom current, or where actual tidal timing runs an hour behind the forecast.)

One more thing: even when all the conditions line up perfectly — neap tide, slack water an hour after the turn, the day's first flood tide still pending — you can still splash in and find visibility under 1 m. That's the ocean for you. Solid training and thorough dive planning remain the only reliable recipe for diving that's both safe and truly enjoyable.