2015 weather highlights Hottest day: 99 degrees, Oct. 9 Coolest days: 59 degrees, Jan. 1-2 and Dec. 28-29 Warmest night: 78 degrees, Sept. 11 Coldest nights: 41 degrees, Jan. 1 and Dec. 27 Wettest day: 1.63 inches, May 14 Days that hit 90 or hotter: Nine (one in March, one in August, three in September and four in October) Daily records for highest maximum temperature set or tied: 10 Daily records for highest minimum temperature set or tied: 23 Odd stat: 2015 was the first year since 1933 when measurable rain was recorded every month of the year in San Diego.

San Diego arguably has never experienced a weirder weather year than 2015. It was as if the calendar were all out of whack.

During periods when the city is usually wet, this past year wasn’t. When it was supposed to be bone dry, the rain came down in buckets. And then it came down some more.

When the city should have been cooling off, it didn’t in 2015, especially at night.

From Jan. 1 to April 30, when the rainfall average in San Diego is 6.85 inches, the city got 1.65 inches. Those first four months of the year were the fourth-driest in city history.

“A ridge (of high pressure) was just off the West Coast,” said Roger Pierce, the meteorologist in charge at the National Weather Service’s office in Rancho Bernardo. “It was steering all the storms around California.”

Then came May, the likes of which San Diego hadn’t seen in nearly a century. Two storms essentially drew a bull’s-eye on San Diego County and missed most of the rest of California. The city recorded 2.39 inches of rain, more than 1,500 percent of the monthly normal — 0.15 of an inch. It was the only time in city history when more rain fell in May than the first four months of the year combined.

Kerah and Brent Farley cut short their walk on the Mission Bay boardwalk on the last day of their vacation and used their parasol as an umbrella to shield their children Damon, 3, and Anderson, 1, from a sudden September downpour. They said this was more of the weather they were used to back home in North Carolina: hot, humid and rainy. — Peggy Peattie

July was an even bigger fluke.

An unusual combination of the remnants of former Hurricane Dolores out in the Pacific and a strong monsoonal flow from the southeast coalesced over San Diego. Torrential downpours on July 18 and 19 drenched the San Diego Pride Parade and rained out the Padres game against the Colorado Rockies. The rain-out was the Padres’ first ever in July.

When it was over, Lindbergh Field, site of the city’s official weather station, had recorded 1.71 inches of rain — by far the most ever during the month. Normal for July is a minuscule 0.03 of an inch. Again, the rest of California got comparatively little precipitation.

Rain clouds looming over downtown San Diego. — John Gastaldo

Equally unusual, and pleasing to some coastal residents but disappointing to others, was the absence of May gray and June gloom. The storms in May and and the persistent high-pressure ridge in June helped wipe out the usually omnipresent marine layer.

The one constant for the year, except for the first couple of days of January and the last two weeks of December, was the warmth.

The first 11 months of 2015 combined were the warmest in San Diego history. But cool days and nights at the end of December knocked the full year into second place on the heat chart, a mere 0.1 of a degree cooler than 2014, the hottest year since monthly temperature records began in town in 1872.

March and October of 2015 were the hottest such months on record; February and September were the second hottest.

The warmest March nights in San Diego history came in 2015. Before this year, no March night had been warmer than 64 degrees. On March 15, the low was 68; it was 66 the next night.

On Sept. 11, the low in town was 78 degrees, matching the record for the highest minimum temperature for any time of year, which had been reached on two September nights in 1984.

On Oct. 10 and 13, the mercury never dipped below 76. Before then, the October record was 73. The week of Oct. 10 to Oct. 16 was by far the warmest week of nights during any October on record.

Pierce said two factors contributed to the warm nights in September and October.

In September, which was also a wet month, monsoonal moisture helped prevent the nights from cooling off. And exceptionally warm waters off the county’s coast, something that had been present most of the year, also kept the adjacent beaches from cooling.

The final two weeks of 2015 seemed quite cool, but only because the previous two years had brought almost unrelenting warmth.

May, with an average temperature that was exactly normal, was the only month in 2015 that wasn’t warmer than normal. The year ended up with 54 days cooler than the climatological norm, five that were exactly normal and 306 that were warmer than normal.

rob.krier@sduniontribune.com | (619) 293-2241 | Twitter: @sdutKrier