Nearly 5,000 unaccompanied immigrant children were caught illegally crossing the U.S. border with Mexico in October, almost double the number from October 2014, according to U.S. Customs and Border Protection data.

Also, in the figures released Tuesday, the number of family members crossing together nearly tripled from October 2014 — from 2,162 to 6,029.

The numbers spiked despite expectations of lower numbers as a result of the colder winter months coming, better enforcement along the border and efforts by Mexican authorities to stem the stream of Central American migrants to the United States. Though tens of thousands of women and children from Central America were caught at the border in summer 2014, it had dropped by nearly half during the 2015 federal fiscal year that ended Sept. 30.

The 4,973 unaccompanied children caught at the border last month is the highest number that Washington-based think tank Washington Office on Latin America has recorded for October since their records began in 2009, said Adam Isacson, a border expert and senior analyst.

The high numbers buck the typical trends of crossings peaking in spring then declining through summer and fall, Isacson said. But there was an uptick in families and children crossing in July, and the numbers have stayed higher than 4,000 each month since.

“Rather than a big jump, it’s been a steady burn,” he said. “I think we are almost in crisis mode with this many months of sustained arrivals.”

Most children and families trying to cross the border in October were from El Salvador. Increased violence in the tiny country, which averaged 30 murders a day in August, is likely partly to blame, Isacson said. Previously, Guatemala had the most families and children apprehended at the border.