Flash Flood — Trujillo Alto, Puerto Rico

2009-09-05 · near Trujillo Alto, Trujillo Alto, Puerto Rico

Event narrative

USGS gage at Rio Grande de Loiza below the dam rose to 29.27 feet, above the flood stage of 22 feet.

Wider weather episode

A tropical wave emerged from the coast of Africa on August 25th, which moved westward near the Cape Verde Islands on the 26th. The system organized as it crossed the Atlantic, developing a low pressure area by the 28th. The system became well-enough organized to be classified a tropical storm during the afternoon of September 1st. A tropical storm watch was issued for the U.S. Virgin Islands and Puerto Rico at 5 pm September 2nd, followed by a tropical storm warning at 11 am on September 3rd. The system moved generally westward, and experienced moderate vertical wind shear through most of its existence as a tropical cyclone. As the surface circulation left most of the associated thunderstorms behind, the system tracked south of due west due to the low-level flow pattern Erika was embedded within. By the 3rd of September, Erika weakened into a tropical depression at 5 pm on September 3rd, and soon devolved into a remnant low during the evening. The remnant disturbance led to heavy rains over the U.S. Virgin Islands and Puerto Rico, which caused flooding in many communities. Minor to moderate flooding was reported in Puerto Rico.The core of the heavy rain fell along the Eastern third of the island.

The hardest hit basin was the Rio Grande de Loiza with a large percentage of its flow coming from the Rio Gurabo one of its larger 'tributaries'. Minor to moderate flooding was reported along the Rio Gurabo, which crested at 23.52 feet ' 5 feet above its flood stage of 18 feet. The Rio Grande de Loiza, which flows from south to north, had a basin average rainfall of 4 to 5 inches with localized rainfall reports of 6 to over 7 inches. This led to a significant rise at the Carraizo Dam, where a number of gates had to be opened to maintain some balance.

View location on OpenStreetMap → (18.3426, -66.0059)

Source: NOAA Storm Events Database, event_id 196822. Narrative written by the NWS forecast office that issued the report.