Two major forest types converge in Connecticut — northern hardwood and central Appalachian hardwood — bringing together yellow birch, maple, beech, sugar maple, hickory, yellow poplar, oak and other varieties of trees, all usually popping into stunning fall foliage that's unique even for New England.

"We have some of the most diverse forests around. There's always something exciting happening. If the oaks are having a bad year, the maples are having a better year," State Forester Chris Martin said. "When everyone sings together, it's pretty spectacular."

But the singing is muted this year.

Peak foliage season for southeastern Connecticut historically begins about Oct. 24, according to the Department of Energy and Environmental Protection. But tree and weather experts say leaf-peepers traveling from all over the U.S. and the globe to the Nutmeg State are looking at roughly a two-week delay this season.

"The warm temperatures we saw this September and October, and well above average rainfall, tells the trees to keep going," Martin said. "Despite short daylight hours, they want to continue to process and stay green."

July, August, September and early October all saw above average temperatures, according to Gary Lessor, a meteorologist and assistant director with The Weather Center at Western Connecticut State University in Danbury. Above average rainfall drenched the region throughout July, September and early October, he added.

"Normally you want things to dry out and you want cool, crisp nights," Lessor said. "We're just not having them."

For most of the year, yellow and orange pigments in leaves are hidden by an abundance of chlorophyll, a green pigment contained in millions of leaf cells where the food-making process required for tree growth occurs. When the cool, dry air of fall comes — particularly lower overnight temperatures, according to Lessor and Martin — the food-making process essentially shuts down, choking off the chlorophyll and giving way to yellows and oranges, according to DEEP.

"Low overnight temperature and everything shutting down quickly is what causes the colors to pop," Martin said. "When you have slower cooling, or no cooling, and they're continuing to grow, and sunlight is less and less, the leaves will turn more brown."

DEEP notes that, "In the presence of bright light, the sugars trapped in the leaves form the red pigments, anthocyanins," and other chemical changes occur, "giving rise to more pigments which vary from yellow to red to blue."

When autumn days "are bright and cool, and the nights chilly but not freezing, the brightest foliage colors will develop. Familiar trees with red or scarlet leaves are red maple, dogwood, red oak, scarlet oak, and sassafras."

But this summer, August's average overnight temperature was 68.3 degrees, which Lessor said was 6 degrees higher than average and "less than ideal" for brilliant fall foliage.

'A big draw'

Even if it's a duller year than usual, Connecticut's $14.7 billion tourism industry still sees a lift from leaf-peeping, with many thousands booking excursions several months in advance at popular foliage hot spots.

"We have senior groups who come for our lunch trains — they start calling in February to book their October trips," said Maureen Quintin, director of communications for Essex Steam Train and Riverboat, which features a fall foliage cruise. "I do think it's a big draw."

Even the warmer weather — a downside for foliage — doesn't hurt the Essex destination in the fall because it leads to more walk-up business, Quintin said.

"A lot of it is just people wanting to be outside," she said. "Once they're out there and having a good time, maybe the foliage isn't the highlight of their day after all. Our fear is the leaves would fall off the trees before they turn."

Terri Almond, the general manager of the Hilton Mystic and a member of the Connecticut Lodging Association board of directors, said September and October is the season of the international traveler, "where New England is such a place to come to for the leaf-peeping."

She noted that within the next week, a group of travel and tourism industry members from Ireland are coming to the Hilton Mystic for a "familiarity tour" to see foliage, Mystic Aquarium, Mystic Seaport and other popular locations in the region. Vineyard and brewery packages are growing in popularity this time of year, she said.

"We've got everything from outdoor active adventures, zip lining through the fall foliage to historical experiences, craft beer and wine farm excursions," said Randy Fiveash, director of the Connecticut Office of Tourism. "Foliage comes to us a little later than other New England states but it stays longer. Not to slam my great friends in Vermont or Maine, where it comes earlier and gets colder faster."

Martin noted that even an average or below average year for foliage "is going to be great already," especially "if you're coming from southern California."

'Spells of windy weather' ahead

While weather impacts foliage on a year-to-year basis, climate change could prove a factor over the long term, according to Martin and Lessor.

Martin noted that trees can't pick themselves up and move like animal species forced to do so due to lost habitats, "so the affects are not as readily apparent."

"But we do see the southern pine beetle coming from Long Island," he said. "At best it's a Mid-Atlantic pest usually. But without the colder temperatures, it flourishes. That critter is here but (a) very low presence."

Martin added that three years of drought, or one year of too much water, throws off the flow "when we could seasonally predict what we could anticipate. What happened to normal?"

Drought in the beginning of 2014, followed by a dry spring in 2015, "got the gypsy moth population rolling," Martin said.

Lessor noted that in the 1970s, the gypsy moth "was extreme and defoliating everything."

"A bacteria came in and the gypsy moths were wiped out," he said. "And 35, 40 years later ... they're finding their way back again."

Martin and Lessor said there's a chance that peak foliage season could fall short just as brilliant colors canopy the roadways and light up the horizons in the coming weeks.

"We could enter peak and then have a good windy rainstorm and you'll have one or two days of peak and everything falls," Martin said.

Lessor said he expected average temperatures over the next week, "so hopefully that can spur the foliage to move a little quicker."

But Lessor warned that "spells of windy weather" are coming.

"As that leaf turns colors, enjoy it. It could be on the ground tomorrow," he said.

b.kail@theday.com