You don't see this too often: There are currently four big tropical cyclones in the Pacific Ocean — the first time that's happened since 2002.

That includes two hurricanes that are on track to hit Hawaii, starting Thursday night:

A note on the names: This map shows two "hurricanes" and two "typhoons" in the Pacific right now. But those are just different names for the same thing. Typhoons and hurricanes are both tropical cyclones — rapidly rotating storms that typically form in warm tropical waters and feature low pressure centers, high winds, and lots of rain.

Hurricanes and typhoons are just different names for the same thing

If the storm originates in the Atlantic or Northeast Pacific, they're called "hurricanes." If they form in the Northwest Pacific, they're called "typhoons." Elsewhere, they're called "cyclones." But it's all the same thing.

Also note that one of those typhoons on the map is a "super typhoon." The definition of a "super typhoon" varies a bit from country to country. The U.S. Navy's Joint Typhoon Warning Center deems a typhoon "super" when the wind speed reaches 130 knots, or 150 miles per hour. That's roughly equivalent to a Category 5 hurricane — really, really massive.

So right now in the Pacific we have:

1) Typhoon Halong: This storm is headed toward southern Japan and is expected to be a roughly Category 1 or Category 2 when it makes landfall.

2) Super Typhoon Genevieve: This is a gigantic storm in the middle of the Pacific that's been wandering around since July 25, when it first appeared west of Hawaii. After losing momentum for a few days, Genevieve has recently strengthened and become a "super typhoon," with maximum sustained winds of 160 miles per hour. The storm appears to be heading northwest, but it's unclear where, exactly, it will end up.

3) Hurricane Iselle: This Category 1 storm is expected to hit Hawaii's Big Island starting on Thursday evening, August 7. "If it does so," writes Capital Weather Gang's Brian McNoldy, "this will be the first hurricane landfall on the Big Island in recorded history."

4) Hurricane Julio: This Category 2 storm is following close on the heels of Iselle — and could hit Hawaii over the weekend or early next week. Hawaii is currently bracing for the impact, with residents stocking up on food and water.

How often does this happen?

It's rare, but not unprecedented, to see four tropical cyclones with winds over 74 miles per hour in the Pacific at once. Over at Capital Weather Gang, Jason Samenow notes that this happened in 1974, 1978, twice in 1990, 1991, 1992, 1993 and 2002.

One reason for the current flurry of storms? The waters in the Pacific are particularly warm right now, with sea surface temperatures in the North Pacific about 1°C warmer than average. That helps fuel stronger storms. (Scientists are also watching to see if an El Niño will form later this year — that officially happens if sea surface temperatures in the southern Pacific rise 0.5°C above their historical average.)

The current situation is much more unusual for Hawaii, though. Even though hurricanes form in the Pacific quite often, Hawaii hasn't been hit by one since 1992 — in part because there's a high-pressure system that usually deflects cyclones and shields the islands. But now Hawaii is on track to get slammed twice in the span of a week.

Further reading: