If Kirk Caldwell were a Pacific hurricane, the weather folks would be calling him a Category Two storm, expected to weaken into a tropical storm by the time it reaches Honolulu.

The race for Honolulu mayor is closing in on its last four weeks with incumbent Caldwell showing a continued weakening, according to new poll numbers.

The Hawaii Poll, taken June 30-July 9 by Ward Research for the Honolulu Star-Advertiser and Hawaii News Now, shows Caldwell trailing challenger Charles Djou, 30 to 39 percent.

The telling measure of Caldwell’s lack of strength is that in January, the Hawaii Poll pitted the 63-year-old Democrat against Councilman Ernie Martin as well as James “Duke” Aiona, and Caldwell lost in both theoretical matchups.

Absolutely no one was talking about Aiona, the former GOP lieutenant governor, who floated a trial balloon for mayor but has since decided not to run for any office this year. Losing to two different candidates shows not that the Caldwell’s opposition is strong, but that Caldwell’s support is barely there.

Two things happened to upset Caldwell’s plans for an easy reelection.

First, Djou, a former GOP state representative, city councilman and U.S. representative, jumped into the race; and then the new leaders of the Honolulu Authority for Rapid Transportation board started revealing numbers showing Caldwell’s rail system has a deficit of at least $1.5 billion.

Caldwell then told the HART board the city doesn’t have the money to build the system past Middle Street, although he wants to find the money to continue the project to Ala Moana Center.

Burrowing into the data shows that a Caldwell confidence gap is developing.

On one hand, 30 percent of the likely voters say they would vote for Caldwell, while 39 percent prefer Djou; but on the other hand, 53 percent say they approve of Caldwell’s job performance, including 60 percent of Americans of Japanese ancestry.

But Caldwell is winning just 34 percent of the AJA vote. January’s poll had Caldwell winning 44 percent of the AJA vote. He also had 49 percent of the Caucasian vote and the latest poll shows Caldwell with just 26 percent. So there is much slippage.

Rail appears to be an important part of Caldwell’s drop in support. In this month’s poll, just 31 percent of likely voters say Caldwell would do the best job “addressing issues related to rail.”

But, 43 percent of the voters say Djou would do the best job.

In all questions asked regarding the election and rail, former Mayor Peter Carlisle came in third.

Four years ago Caldwell was the construction industry’s guy. The construction industry and unions slammed Caldwell’s opponent, former Gov. Ben Cayetano, with such misleading slanderous ads and commercials that Cayetano was able to force an apology from the Pacific Resource Partnership political action group.

Today, Djou, with his moderate message of build rail but control costs, appears to be winning both union support and voters.

Caldwell needs to switch the discussion. If the race for mayor settles on rail as the only issue, Caldwell will have little to campaign on. But if he can change the conversation, he can still salvage a campaign that is slipping away.

Richard Borreca writes on politics on Sundays, Tuesdays and Fridays. Reach him at rborreca@staradvertiser.com.