Climate Notes June/July 2008

June 2008 was an atypically dry month across Puerto Rico. While statistically speaking the month of June is the fifth driest month of the year, islandwide, June 2008 was significantly drier than average. Unlike May when the north coast of Puerto Rico received above normal precipitation, no section of Puerto Rico received above normal rainfall during the month of June. At the Luis Muñoz International Airport in San Juan, 5.31 inches of rain fell in June, which was actually 1.00” above normal, but this number was skewed by two very wet days at the beginning of the month, during which the ASOS received 3.56 inches in fairly isolated rainfall events associated with streamers coming off the El Yunque rainforest. The wettest June on record was June 1965, when 10.96” of rain fell, and the driest June on record was June 1985, when only 0.29” of rainfall was recorded. Temperatures in San Juan averaged 82.8ºF, which was 0.5ºF warmer than the 52 year average for the month, making June the second consecutive above normal month, in terms of temperature, across San Juan.

Islandwide, Puerto Rico received, on average, approximately 1.97 inches less rainfall than normal, or only 62% of the normal value, for the month of June. This represents a deficit of rainfall of 4.27 inches for the months of May and June combined! At the end of the month, the only section of the island that remained above normal year to date (YTD) was the north coast, which as of July 4 th, had received 105% of its normal rainfall YTD. Overall, the entire island stood at only 69% of the average rainfall YTD. As a result, it was of no surprise that the most recent U.S. Drought Monitor graphic of Puerto Rico continued to classify almost the entire southern half of Puerto Rico as being abnormally dry (see graphic below or visit the Climate Prediction Center (CPC) for more information). Some of the highest temperatures recorded for the month were 97ºF, reported in Ponce on June 26 th, 94ºF, reported in Lajas on June 26 th, 94ºF, reported in Gurabo on June 22 nd, 94ºF reported in San Juan on June 17 th, and 93ºF reported in numerous locations. The coolest temperature recorded during the month of June was 58ºF, recorded in Adjuntas on June 4 th.

Looking ahead, July is the 6 th wettest month across Puerto Rico, with the Luis Muñoz International Airport in San Juan receiving 4.81” of rainfall on average*. A record 9.35” of rain fell in July 1961 and the driest July on record was July 1974, when only 1.12” of rainfall was recorded in San Juan. The average high temperature at the Luis Muñoz International Airport in San Juan for July is 82.5 ºF*, making July the 2 nd warmest month of the year, second only to August. Presently, the Tropical Pacific is experiencing ENSO-neutral conditions and these conditions are expected to continue through at least the fall of 2008 which contribute to the 90% probability of and near of above normally active hurricane season forecast by NOAA.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/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 *