Flood in Puerto Rico, November 12 to 15, 2004

A persistent upper trough to the west of Puerto Rico and a extremely moist low level air mass, brought numerous showers during the period from November 12-15. On the 12 November rainfall was already fairly impressive across the eastern and central interior, although the northeast quarter of the island received 1 to 2 inch rains. Reports of flooding were received from Toa Baja, along the River Cibuco in Vega Alta. Moderate to occasionally heavy rains persisted throughout much of the 12th under strong north to northeast surface wins that produced substantial orographic enhancement over the foothills and mountains of central and eastern Puerto Rico. Rainfall intensity remained fairly low, but the persistence produced impressive totals in these areas, with 3 to 6 inches across a huge swath of central Puerto Rico through 8 am on 13 November. Flood warnings were issued Rio Grande De Arecibo, Rio Grande De Manati, Rio De La Plata and Rio De Bayamon and remained in effect for up to two days in some locations. The high surf and north winds along the coast hindered normal discharge of rivers into the sea, exacerbating the flood situation. The activity continued to be widespread and intense on 13 November. Flash Flood Warnings were isued for 14 northeast municipalities from Fajardo southwest to Gurabo and Juncos. Reports of flash flooding became more numerous throughout the day and another Flash Flood Warning was issued for 7 municipalities in the central mountains in the afternoon. This warning was extended in the evening as moderate to heavy rainfall persisted across the same area. Numerous landslides were also reported at this time, especially in Cayey, Aguas Buenas and Naranjito. Bridges were reported overtopped, collapsed or washed out in several locations, including Naranjito, Orocovis, Morovis, Aguas Buenas, Cidra, and Utuado. Another Flash Flood Warning was issued for Dorado and Toa Baja, primarily in the highly saturated Rio De La Plata basin during the evening. 24-hour rainfall ending 800 am on 14 November was very similar to the previous day's total, with highest amounts, in excess of 5 inches, centered in the area around Comerio, Aibonito and Aguas Buenas. November 14 saw little break in the rainfall activity as the upper trough remained stationary to the west of the island and the very strong and moist northeast flow continued advecting showers across the island. Rainfall intensity remained moderate throughout much of this event. Nonetheless, the persistent moderate rainfall appears to have been ideal for the production of landslides around the island. Landslides covered numerous roads and several damaged or collapsed bridges were also reported. Around 100 pm on 14 November a landslide in Adjuntas, Barrio Yahuecas, pushed a vehicle with three persons into the River Rio Blanco, causing a 28-year old man to drown and injuring two young women. A direct flood death occurred in Guaynabo around the same time when a 74-year old women was reportedly swept into the River Rio Guaynabo. Meanwhile, Flood Warnings remained in effect for many of the river basins draining the northern slopes of the central mountains. The most intense rains on 14 November occurred over the east central and southeast parts of the island, prompting a Flash Flood Warning for 10 municipalities in that region. During the late afternoon overnight hours of 14 November the heaviest rains fell across the Culebra, Vieques. Flood Warnings along the Rio Cibuco, Rio De La Plata, Rio Grande De Manati and Rio Grande De Arecibo continued into 15 November, as the strong onshore flow continued to restrict outflow of these rivers into the Atlantic Ocean. Rainfall amounts were much less than previous days however, with only isolated amounts in excess of one inch and many locations dry for the first time in nearly a week. River flooding from this event was significant but actually quite ordinary by Puerto Rico standards and was considerably less than during Tropical Storm Jeanne in September 2004. The rainfall and subsequent flooding was also somewhat less than occurred in November 2003, which affected a larger area and had higher rainfall amounts.