Global Analysis - May 1999
larger image Preliminary mean monthly temperature anomalies (using a base period 1880-1998) for May are shown in the figure to the left. Land and ocean temperatures remained above the long term mean in May 1999, but they did not approach the record values recorded in May 1998. The average temperature over land and ocean was 0.31 C above the mean, well below the record anomaly recorded last year and only the 5th warmest May this decade. As seen in previous months, the most dramatic cooling occurred over the oceans. The sea surface temperature anomaly fell from 0.57 C in May 1998 to 0.21 C in 1999. Global land temperatures averaged 0.54 C above the long term mean in May 1999, 0.42 C cooler than in May 1998.
The trend toward cooler land and ocean temperatures began mid year last year as El Niño gave way to La Niña. This figure shows the difference in land surface temperatures between May 1998 and May 1999. (These are NOT temperature anomalies. They are simply May 1999 temperatures minus May 1998 temperatures.) Blue dots indicate cooler temperatures in 1999. Some areas were warmer, but blue dots dominate the map, indicating that temperatures were cooler throughout most parts of the world in 1999.
larger image This figure of global anomalies shows that temperatures were still well above average in May 1999 throughout much of the world. The largest positive anomalies (greater than 4 C above average) occurred throughout the eastern half of Canada, parts of eastern Europe and the Mediterranean as well as much of central Russia. Other areas that experienced above average temperatures included Australia as well as areas of the Far East, and most of Mexico.
A trend toward near average temperatures continued in the western half of Canada after a much warmer than average winter season. Temperatures were near average to slightly above average in the eastern half of the United States while parts of the western United States were as much as 4 C cooler than average. Much of western Russia also experienced below average temperatures in May. See the U.S. Regional / Statewide Analyses pages and the Global Regional Analyses pages for more details on regional climate in the United States and throughout the world.
As shown in the adjacent figure, global precipitation (land only) averaged near or slightly below the long term mean (1900-1998) indicating global reporting stations were generally drier than average in May. This was the first month in 1999 that global precipitation was below the long term average.
larger image Many islands in the South Pacific received above average precipitation throughout the first four months of the year but were much drier than average in May. The South American countries of Venezula and Guyana were also much drier than average. Precipitation in these areas was as much as 100 mm (4 inches) below average. Dry conditions also prevailed across eastern and western areas of the United States, northern sections of Australia, eastern Europe and the grasslands and tropical forests of western Africa. Small negative anomalies are also spread throughout a large portion of Russia.
A trend to wetter conditions that began last month in much of southern China continued in May. Anomalies greater than 50 mm (2 inches) above average are shown in areas that had been experiencing drought conditions throughout much of their fall and winter seasons. Areas of southern India also received much above average precipitation in May as the monsoon season got an early start. Above average precipitation also fell in parts of Europe, Argentina, the central United States, and southern Canada.
Greatest positive surface wetness anomalies were observed across the central plains of the United States, portions of central and eastern Canada, parts of central Russia and a good deal of Laos, Cambodia and Thailand. There were small positive anomalies in central Argentina, northern South America, and portions of southeast Africa. The largest negative anomalies were across portions of Argentina, northern Russia, the Middle East and across eastern Australia. Scattered negative wetness anomalies covered portions of the United States, Canada, Russia, and portions of Africa.