For the recreational athlete, September in Hawai'i offers not just an embarrassment of riches but a bedevilment of decisions.

What will it be for Labor Day weekend: 30-mile romp through tropical rain forest or a 2.4-mile swim in the open ocean? Both, perhaps?

If cycling is the thing, do you opt for a 112-mile, round-the-island blitz at Lance Armstrong intensity or a 100-mile ride in Sheryl Crow cruise control?

You could try the tri, but what would you choose, an all-woman sprint triathlon or an old-school Ironman broken up over three separate weekends?

"You have to make choices," says Beth Moriwake, a 34-year-old retail manager and veteran of many action-packed Septembers. "It's tempting to try and do everything, but you have to be careful you don't break your body — or your checkbook."

Even in Hawai'i, where year-round temperate weather allows for a full calendar of on- and off-road races, the month of September is remarkable for its concentration of high-profile events — from the Waikiki Roughwater Swim to the Hana Relay, the Honolulu Century Ride to the Na Wahine Sprint Triathlon.

The month kicks off with the state's oldest, continuous trail run: the Tantalus Trek and Triple Trek. Race director PJ Salmonson expects about 150 people to tackle the 10-mile, figure-8 course along the Makiki-Tantalus trail system. With more than 2,000 feet of elevation to gain and a heart-in-mouth descent down the gnarly, rooty "Hogsback" path, the course is as formidable as it is beautiful — especially for the 40 or so runners who plan to run it three times for a total of 50 kilometers (roughly 30 miles).

Most of the runners will take advantage of the last running of the 10-mile race.

"When we put it together, the idea was to introduce people to trail running," Salmonson said. "I think we've accomplished that."

The Hawaiian Ultra Running Team (HURT), which hosts the race, will now focus its attention on its 100-mile race in January and a series of low-frills trail runs throughout the year.

Each year an ambitious — masochistic? — few attempt September's most ambitious back-to-back — the Tantalus Trek on Saturday and the 2.4-mile Waikiki Roughwater Swim on Sunday.

The Waikiki Roughwater Swim is traditionally the largest swimming event in the state. Last year, nearly 900 people entered the race.

"A lot of people don't feel confident trashing their legs one day then doing the Roughwater the next," Salmonson said. "But some don't even care."

Moriwake tried it four years ago and learned a painful lesson.

"It's possible," said Moriwake, who did well in the trail run but barely finished the roughwater swim before the cutoff time. "But it really isn't fun."

And Hawai'i's multisport athletes want to be sure that they have something left for the rest of the month.

The state's two biggest cycling events — the competitive Dick Evans Memorial Road Race and the non-competitive Honolulu Century Ride — both take place this month.

Each race attracts both serious cyclists and athletes from other sports — like last year's Waikiki Roughwater Swim winner Noa Sakamoto — looking to supplement their training.

Dick Evans race director Barry Sullivan said that rather than diminishing each other's fields, the two races complement each other well, providing full coverage of the local cycling community.

"They volunteer with us and a lot of our teams will volunteer to help with the Century Ride," Sullivan said.

Many athletes training for the October's Ironman Triathlon Word Championships in Kona make it a point to gauge their progress at the Waikiki Roughwater Swim and the Dick Evans Memorial Road Race — two of the original races (along with the Honolulu Marathon) upon which the first ironman triathlon was based.

Some athletes who aren't quite ready to pull off an Ironman in one day combine the two events with the Maui Marathon for a watered-down taste of what it's like.

Johnny Landeza, vice president of the Mid-Pacific Road Runners Club, said soldiers returning from Iraq and Afghanistan may be partly responsible for a recent surge in road race participation.

Last month's Norman Tamanaha 15K attracted about 800 entrants, of whom nearly 700 finished the race. That's a major spike over last year, when the first race in the club's Marathon Readiness Series drew only 400 runners.

The Marathon Readiness Series was organized several years ago to help runners prepare for the Honolulu Marathon in December. This year, some 600 people signed up in advance for all five races.

Landeza said he expects the next two races in the series, the Kalaeloa 20K and the Schofield Barracks 25K, to draw well, despite all of the other activity this month.

Landeza himself will be occupied with the Kalaeloa 20K on Sunday, the Hana Relay next week Saturday, and the Schofield Barracks 25K the next weekend.

"It crossed my mind to do the Ko Olina Triathlon the next weekend (Oct. 1-2)," he said. "But I think that would be too much."

Valley Isle Road Runners has two major events this month.

The Maui Marathon is a consistently popular draw with its picturesque course along Maui's western shores offering the added bonus of prime whale spotting.

The Hana Relay, now in its 34th year, is also a perennial favorite. Race director Joe Alueta expects about 100 six-person teams to line up for the 52-mile relay race from Kahului Airport to Hana Ball Park.

"This is a race where you have teams that are really serious and teams that are just really goofy and want to have fun," Alueta said. "There are people who don't do any other race, but they do this one every year."

The relay typically attracts large contingents from O'ahu and the Big Island, and the competition in the mixed and men's masters divisions is as fierce as any race in the state.

"The problem is there are so many people doing the event that we have a hard time getting enough volunteers from our group," Alueta said, laughing. "Whoever happens to be injured gets drafted to help out."

Alueta said interest in triathlon and other multisport activities has led to a more diverse mix of events statewide.

"It helps us as a community because it keeps people active all year round," he said.

The relative newbie of the September bunch is the Na Wahine Sprint Triathlon — an all-women's event sponsored by the Try Fitness! training group that accommodates seasoned pros and absolute beginners.

Try Fitness! chose to stage the event in September to coincide with Women's Health Month. Participation has steadily grown from 129 seven years ago to an estimated 300 this year. Director KC Carlberg encourages Try Fitness! members to participate in a variety of races to test their skills and build their confidence.

In September, they soon learn, it pays to pace. "It's a busy month," Carlberg said. "It's the culmination of a lot of training over the summer."

Reach Michael Tsai at mtsai@honoluluadvertiser.com.