The performance of US prime jumbo loan performance within residential mortgage-backed securities (RMBS) slipped again in January as serious delinquencies (60+ days past due) rose for the 32nd consecutive month and edged closer to 10%, according to the latest market commentary from Fitch Ratings.

Prime jumbo loan delinquencies began to rise in Q207 but accelerated since then. In 2009, the rate of delinquency nearly tripled during the year. The serious delinquencies rose to 9.6% in December from 9.2% in November.

“The new year has brought no relief from declining jumbo loan performance,” said Fitch managing director Vincent Barberio. “The trend line for delinquencies indicates the 10% level could be reached as early as next month.”

Fitch indicated delinquency rates on pre-2005 vintages are still lower than recent vintages. But seasoned RMBS pools have deteriorated over the last year, rising to 4.3% in serious delinquency from 1.8%. Of all prime jumbo senior RMBS classes issued before 2005, about 40% are under a negative rating outlook due to weak collateral performance, despite only 5% having experienced downgrades so far.

The roll rate of prime jumbo borrowers that fell into delinquency declined slightly to 1.2% for January from the seasonal high of 1.3% in December, Fitch said.

Write to Diana Golobay.