and warmer air to the northern half of North America. For example, in an El Niño winter, an extended North Pacific jet stream tends to bring more storms across the southern tier of the U.S. The Hadley circulation is connected with the jet streams over the middle to high latitudes, which steer storms around the world and separate cold and warm air masses.Īs El Niño heats the atmosphere above the central and eastern tropical Pacific, it leads to a stronger Hadley circulation and changes to the jet streams. In a one-paragraph nutshell: warm air that rises near the equator moves toward the poles high up in the atmosphere, descending again near 30 °N and 30 °S, in an overturning pattern called the Hadley circulation. We spend so much time and energy studying and forecasting El Niño (and its counterpart, La Niña) because those changes to the atmospheric circulation have global impacts. Both measured -1.0 standard deviations in May (meaning the indexes were lower than about two-thirds of all measurements), providing significant indication of the weaker Walker circulation and further evidence that the ocean-atmosphere system has coupled and El Niño conditions have developed. We quantify the atmospheric component of El Niño using the Equatorial Southern Oscillation Index ( EQSOI) and the Southern Oscillation Index ( SOI), both of which compare the surface atmospheric pressure in the western Pacific to that in the eastern Pacific (more details on these indexes here). Convection over Indonesia was reduced, too, another characteristic of the weaker Walker circulation. Over the past month, evidence of the weakened Walker circulation appeared in the form of weaker trade winds over the western Pacific and more clouds and rain over the equatorial Pacific. Anomalous ocean warming in the central and eastern Pacific (orange) help to shift a rising branch of the Walker Circulation to east of 180°, while sinking branches shift to over the Maritime continent and northern South America. Generalized Walker Circulation (December-February) anomaly during El Niño events, overlaid on map of average sea surface temperature anomalies. These strong surface winds help to keep the warm water piled up in the western Pacific. The average Walker circulation is characterized by rising air and storms (convection) over the very warm waters of the far western Pacific, west-to-east winds high up in the atmosphere, descending motion over the relatively cooler waters of the eastern Pacific, and the trade winds-east-to-west surface winds. The third criteria, “indications of a weaker Walker circulation,” refers to the average atmospheric pattern over the equatorial Pacific. We anticipate that it will remain above this El Niño threshold for the next several months, based on climate model predictions and current conditions in the tropical Pacific (more on this in a minute)… check! There are the first two of our three rings criteria. NOAA, based on Coral Reef Watch maps available from NOAA View. A higher-resolution version of this animation is available as a movie. The waters in the key monitoring region, which scientists call "the Niño-3.4 region," start out cooler than average (blue) and progressively become warmer than average (red) as La Niña ends and El Niño arrives. Straight-line winds and large hail will be the main threats.Animation of maps of sea surface temperatures in the Pacific Ocean compared to the long-term average over five-day periods from the end of January to early June 2023. Redevelopment of strong to severe thunderstorms along with torrential rainfall is expected generally south of Hwy 80 – I-85 between 1 pm and 8 pm Thursday. In addition, torrential rainfall could lead to flash flooding and Flood Watches are in effect across much of the state into Thursday. Within 50 miles of either side of this line, numerous storms are possible on an almost continuous basis through the night.įor the remainder of this afternoon through this evening near and south of I-20, the potential continues for a few tornadoes including EF2+, pockets of straight-line wind gusts of 80 mph causing significant damage and hail up to baseball size. The exception may near a nearly stationary boundary stretching from near a Tuscaloosa – Montgomery – Eufaula line. It should be noted that there will likely be 2-4 hour lulls between each wave of storms through tonight. There are little changes to the SPC outlook area, and I have included a timeline for severe weather through early Thursday morning. By Jim Stefkovich, Meteorologist, Alabama Emergency Management AgencyĬLANTON – Wednesday, 2:30 pm June 14, 2023Ī couple of tornadoes have been reported as of early afternoon in southeastern AL, with a number of damaging wind gusts near and north of I-20.
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