Climatological Background In May, the sun is well into its march north of the equator (the maximum northward location will be achieved in June at 23.6 degrees north). Surface heating of the continents are setting the stage for summer monsoonal systems or northern hemisphere warm season rains. The lack of direct solar heating in the southern hemisphere creates a north-south temperature difference which strengthens mid-latitude storm tracks and the approach of winter.

Monthly Mean Temperature (1961-1990), data from the Climate Research Unit, University of East Anglia

Monthly Mean Precipitation (1961-1990), with data from the Climate Research Unit, University of East Anglia

Temperatures Over Land
Europe:   Above-average temperatures were observed across much of west-central sections for the fourth consecutive month.    
Asia:  Temperatures continued above average in a broad west-east band extending from Iran in the west to coastal China in the east as well as in north-central sections of the Former Soviet Union.  In contrast, temperatures were as much as 4 C below average across much of south-central Russia. Temperatures were near to slightly below average across India and most of southeast Asia. 
Africa:  With the exception of southern Africa - southward of Botswana and Zimbabwe - which had near-average conditions, most of the remainder of the continent experienced above average temperatures.
Australia: Eastern Queensland and New South Wales experienced near-average conditions for the month but temperatures were well below average elsewhere.  In fact, (maximum) temperatures for the month were the lowest recorded for Australia as a whole.
South America:  Uneventful as far as temperatures were concerned, near average conditions prevailed across most of the continent.  
North and Central America:  Most of the south-central United States  and north-central Mexico observed above average temperatures.  Temperatures averaged 1 to 2C below average across the Canadian Prairies as well as north-central Alaska.  Conditions were close to average elsewhere.
 
 

Temperature Difference from the 1961-1990 mean, with data from NCEP Climate Prediction Center, CAMS.

Precipitation
Africa:  Below-average rainfall persisted over much of eastern Africa from southern Ethiopia southward into Kenya, southern Somalia and much of Tanzania.  Above average precipitation was observed in western Zaire and northwest Angola as well as portions of eastern South Africa and  Zimbabwe.  The rainy season began in western Africa with above average rainfall across western Ghana, southern Mali and Burkina Faso and unusually dry conditions farther east from Nigeria into northern Cameroon.  
Australia:  Exceptionally dry conditions were observed in southern portions of Western Australia.  Although the spatial coverage of the real-time observations below are limited, analysis by the Australian Bureau of Meteorology indicates unusually heavy rains fell in south-central Queensland southward through New South Wales to Tasmania.  Heavy rains also occurred in northern sections of the Northern Territory.
Philippines / Indonesia:    Above average rainfall was observed throughout the region with localized very heavy rains in Timor and New Guinea.
Southeast Asia:  Precipitation was above average from Bangladesh southeastward  through Burma and Thailand and into Cambodia.
China:   Below average rainfall was observed across the North China Plain.  Locally heavy rains in west central sections resulted in above average rainfall for the month.
South America:  Uruguay and eastern Argentina saw above average rainfall during May.  Above average precipitation was also observed in Ecuador, Colombia and along the northern border of Brazil and neighboring areas.  Below average rainfall occurred over south-central Brazil.  Extremely dry conditions were seen in the area around Sao Paulo with the start of the dry season there just beginning.
Middle East: Rainfall continued to be below average across much of the Middle East eastward to Afghanistan and Pakistan. 
Central and North America:  Heavy rainfall was observed across southern Mexico southward into Guatemala. Below average rainfall continued in the southeastern US and along the Gulf coast.  Heavy rains in the midwestern US brought some temporary relief to drought conditions there while the northeast also had above average rainfall. 
Europe:  Northern and western Europe had above average precipitation for the month while unusually dry weather was observed across eastern and southern Europe from southern Poland southward to the Mediterranean Sea.

Precipitation Difference from 1961-1990 mean, with data from NCEP Climate Prediction Center, CAMS-OPI.

Oceanic Conditions
 Tropics: Weak La Niña (colder than average) conditions continue in the central equatorial Pacific. The large positive anomalies of last month in the eastern equatorial Pacific have weakened. Neither oceanic observations nor model predictions suggest a transition towards warmer than average contions (El Niño) in the coming months.
 Extratropics: The most notable feature of the extratropical oceans continues to be the large positive anomalies in the Northern Hemisphere mid-latitudes (e.g., +4 C off the northern coast of Japan).

Monthly Sea Surface Temperature Difference from the 1950-1979 mean, with data from the Environmental Modeling Center, NCEP/NOAA.