Note: The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. Effective September 2012, the GHCN-M version 3.2.0 dataset of monthly mean temperature replaced the GHCN-M version 3.1.0 monthly mean temperature dataset. Beginning with the August 2012 Global monthly State of the Climate Report, released on September 17, 2012, GHCN-M version 3.2.0 is used for NCDC climate monitoring activities, including calculation of global land surface temperature anomalies and trends. For more information about this newest version, please see the GHCN-M version 3.2.0 Technical Report.
*The GHCN-M version 3.1.0 Technical Report was revised on September 5, 2012 to accurately reflect the changes incorporated in that version. Previously that report incorrectly included discussion of changes to the Pairwise Homogeneity Algorithm (PHA). Changes to the PHA are included in version 3.2.0 and described in the version 3.2.0 Technical Report. Please see the Frequently Asked Questions to learn more about this update.
Temperature
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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. |
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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. |
Precipitation
| 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. |
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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. |
Global Surface Wetness
| 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. |
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