Climate Notes April/May 2008

April 2008 brought some much need rainfall to Puerto Rico. This is typically the case as April generally marks the transition to the rainy season here in Puerto Rico. While statistically speaking the month of April is much wetter than March, this is not always the case. In April 1997, only 0.08” of rainfall was recorded at the Luis Muñoz International Airport in San Juan, one of the driest months on record. On average, 4.17* inches of rainfall accumulates at the Luis Muñoz International Airport in April, with April 2008 bringing an official total of 4.86 inches. By the end of the month, the airport had received a total of 14.38”, or 122%* of normal rainfall year to date. Temperatures in April averaged 78.9 ºF, which was 0.5 ºF cooler than the 52 year average for the month

Islandwide, Puerto Rico received, on average, approximately 0.37" more rainfall than normal, or 107% of the normal value, for the month of April.  The first and last weeks of April accounted heavily for the above normal rainfall for the month, with a mid to upper level trough helping to induce several low level disturbances that spread across the island during those weeks. By the end of April, Puerto Rico's rainfall had risen to 88% of the average year-to-date, prompting the U.S. Drought Monitor to reduce the area of Puerto Rico classified as being abnormally dry (see graphic below or visit the Climate Prediction Center (CPC) for more information). The above normal rainfall across Puerto Rico for the month of April was a bit misleading, as the intense rainfall that fell during the first and last weeks of the month was saddled by 3 very dry weeks with intermittent periods of dust laden Saharan air passing across the island. The highest maximum temperature recorded for the month was 92 degrees F, reported both in Ponce on the 29 th and San Juan on the 23 rd, while the coolest temperature recorded for the month was 53 degrees F, reported in Gurabo on the 12 th of April.

At the Luis Muñoz International Airport in San Juan, the average monthly temperature was 78.9 ºF*, which was -0.5 ºF lower than average, with a maximum temperature of 92 ºF, reported on the 23 rd of the month, and a minimum temperature of 71 ºF, reported multiple times. This marked the 4 th straight month that below average temperatures were recorded in San Juan. A total of 4.86 inches of rainfall was reported at the Luis Muñoz International Airport, which was 0.69” inches above normal, well shy of the record 15.00” recorded in April, 2005. The driest April on record was April 1997, when only 0.08” of rainfall was recorded.

Looking ahead, May is one of the wetter months across Puerto Rico, with the Luis Muñoz International Airport in San Juan receiving 5.71” of rainfall on average*, with a record of 14.99” received in May 1965. The driest May on record was May 1972, when 0.44” of rainfall was recorded in San Juan. The average high temperature at the Luis Muñoz International Airport in San Juan for May is 80.9 ºF*, 1.5 ºF warmer than April. Presently, La Niña conditions are expected to continue for the next three months.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_disc_apr2008/ensodisc.pdf

* All climate averages for San Juan taken from 52 continuous year period of 1956-2007 which differ from the 30-year average used in official climate reports *