U.S. flag An official website of the United States government.
Official websites use .gov

A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS

A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

i

Climate Assessment for 1999



Details

  • Journal Title:
    Bulletin of the American Meteorological Society
  • Personal Author:
  • NOAA Program & Office:
    NESDIS (National Environmental Satellite, Data, and Information Service)
  • Description:
    The global climate during 1999 was impacted by Pacific cold episode (La Niña) conditions throughout the year, which resulted in regional precipitation and atmospheric circulation patterns across the Pacific Ocean and the Americas that are generally consistent with those observed during past cold episodes. The primary La Niña–related precipitation anomalies included 1) increased rainfall across Indonesia, and a nearly complete disappearance of rainfall across the east-central and eastern equatorial Pacific; 2) above-normal rains across northwestern and northern Australia; 3) increased monsoon rains across the Sahel region of western Africa; 4) above-average rains over southeastern Africa, 5) above-average rains over the Caribbean Sea and portions of Central America, and 6) below-average rains in southeastern South America. The La Niña also contributed to persistent cyclonic circulation anomalies in the subtropics of both hemispheres, which flanked the area of suppressed convective activity over the eastern half of the equatorial Pacific. In the Northern Hemisphere this anomaly feature contributed to a pronounced westward retraction of the wintertime East Asian jet stream, which subsequently impacted precipitation and storm patterns across the eastern North Pacific and western North America. The La Niña–related pattern of tropical rainfall also contributed to a very persistent pattern of anticyclonic circulation anomalies in the middle latitude of both hemispheres, extending from the eastern Pacific across the Atlantic and Africa eastward to Australasia. This anomaly pattern was associated with an active Atlantic hurricane season, an inactive eastern North Pacific hurricane season, above-average rains in the African Sahel, and an overall amplification of the entire southeast Asian summer monsoon complex. The active 1999 North Atlantic hurricane season featured 12 named storms, 8 of which became hurricanes, and 5 of which became intense hurricanes. The peak of activity during mid-August–October was accompanied by low vertical wind shear across the central and western Atlantic, along with both a favorable structure and location of the African easterly jet. In contrast, only 9 tropical storms formed over the eastern North Pacific during the year, making it one of the most inactive years for that region in the historical record. This relative inactivity was linked to a persistent pattern of high vertical wind shear that covered much of the main development region of the eastern North Pacific.
  • Keywords:
  • Source:
    Bulletin of the American Meteorological Society, 81(6), S1-S50.
  • Series:
    State of the Climate
  • DOI:
  • Document Type:
    Journal Article
  • Rights Information:
    Other
  • Compliance:
    Library
  • Main Document Checksum:
    urn:sha256:d9fefe0bba5353c12aeb58c9cb1dabb042a7bb8457ad8adf5ddee19220fdbe30
  • Download URL:
  • File Type:
    Filetype[PDF - 2.38 MB ]

Related Documents

PREVIOUS
ON THIS PAGE
Details Related Documents
The NOAA IR serves as an archival repository of NOAA-published products including scientific findings, journal articles, guidelines, recommendations, or other information authored or co-authored by NOAA or funded partners. As a repository, the NOAA IR retains documents in their original published format to ensure public access to scientific information.
BACK TO TOP