ENFEN OFFICIAL STATEMENT N Status Warning System: El Niño Coastal Alert 1

Transcription

1 ENFEN OFFICIAL STATEMENT N Status Warning System: El Niño Coastal Alert 1 Note: This translation is provided for convenience, the official version is in Spanish The Multisectoral Committee of the National Study of El Niño (ENFEN) maintains the state of alert due to the strong El Niño that has been developing in the Peruvian coast with above-normal temperatures. Occasional "very strong" 2 rainfall events could be expected in the Tumbes and Piura regions in late December and January. It is likely that the strong warm conditions will extend to January. However, the probabilities for the magnitude of the coastal El Niño reached through March 2016 are estimated as 50% for moderate and 35% for strong. The Committee of the National Study of El Niño (ENFEN) met to review and update the information on weather, oceanographic, biological-fishing and hydrological conditions of November and assess its perspectives. The warm phase of the Southern Oscillation Niño continues. In November, the Sea Surface Temperature (SST) in the Central Equatorial Pacific (Niño 3.4) 3 showed values above those observed in 1997 and 1982 (see Figure 1). However, rainfall in the central and eastern Equatorial Pacific, a key indicator of the atmosphere-ocean coupling, increased but did not reach the values observed in 1997 and Also, westerlies wind bursts were not observed in the Central Equatorial Pacific that could produce new downwelling Kelvin waves. The thermocline depth and mean sea level (MSL) anomaly, in November, showed evidence of the downwelling Kelvin wave, which deepened the thermocline by 40 meters and increased the mean sea level (MSL) between +9 and +17 cm, on average, in the Niño 3 4 region. In November, the MSL on the northern coast of Peru was +18 cm above its normal, while in the central and southern coast the anomalies were +12 cm. The SST anomalies was C in the north coast and +1.8 C in the central coast, these values were smaller than in October. 1 Definition of Coastal El Niño Alert: According to recent conditions using expert judgment in a collegial manner, the ENFEN Committee considers that Coastal El Niño event has begun and/or ICEN value indicates warmer conditions, and is expected that Coastal El Niño consolidates (ENFEN Technical Note N ). 2 Heavy rainfall: Those that exceed the threshold of the 95th percentile (approximately mm / day for December and January) 3 Niño Region 3.4: 5 S - 5 N, 170 W W. 1 Niño Region 3: 5 N-5 S, 150 W-90 W

2 SST and MSL were observed to increase in the last week of November, mainly along the northern coast (by at least +30 cm and + 3 C, respectively, in Paita and Talara), while in the Paita fixed station, located seven nautical miles off the coast, the ocean temperature anomaly increased to +4 C in the first 100 meters and up to +5 C in the first 60 meters, due to the arrival of the downwelling equatorial Kelvin wave. The maximum and minimum air temperatures remained above normal, with anomalies of +1.9 C in both cases, along the northern and central coast, while the southerly and southeasterly coastal winds continued intense due to the strengthening of the South Pacific anticyclone (1026 hpa at its core, normal: 1022 hpa), which presented cold characteristics that favored the presence of migratory highs. The Coastal El Niño Index (ICEN) for October was C, maintaining the category of strong warm conditions. The river flows on the Peruvian coast in November were normal in the northern region, with the exception of the Chancay-Lambayeque and Chira rivers, which were higher than normal; this was the result of rainfall that occurred in their middle and upper basins. In the southern region, flows they were below their average. The reservoirs in the northern and southern coast had 45% and 43%, respectively, of theur maximum capacity. The decrease relative to the previous month is a consequence of agricultural use. The anchovy was distributed within 50 miles from the coast, between Chimbote and Bahia Independencia. The reproductive indices indicated the declination of the main spawning period. Also, their vertical distribution was moderately deeper than normal. PERSPECTIVES The downwelling Kelvin wave generated by the westerly wind anomalies during September and October in the Central Pacific, is expected to maintain or increase the Niño 1+2 SST anomaly, without exceeding, on average, +2.5 C during December 2015 and January 2016, which would maintain the strong Coastal El Niño conditions. The arrival of the Kelvin wave will also increase the MSL, SST, thermocline depth and air temperature, mainly in the northern and central coast of Peru. Also, the occurrence of occasional "very strong" rain is expected in Tumbes and Piura, in late December and January. For the central equatorial Pacific (Niño 3.4), global models continue to predict that El Niño would reach a very strong magnitude through 2015, after which it would decline over the first months of Most of the prediction of global models for the eastern Pacific (Niño 1+2) indicate that the Coastal El Niño will remain strong until December. From January to March 2016, most models predict a moderate magnitude of the Coastal El Niño.

3 For rainfall in the Andes and the Amazon, El Niño in the central Pacific implies the possibility of reduced rainfall in the austral summer, without being determining, especially in the southern highlands. For the update of the Coastal El Niño forecast for the summer , the ENFEN Committee considered, among other things, that: - The SST anomaly in the Niño 1+2 was below that observed in November 1982 and 1997 (see Figure 1b). - The current downwelling Kelvin wave is not expected to increase the SST anomaly in the Niño 1+2 above +2.5 C in the following two months. - There is no evidence of new intense equatorial downwelling Kelvin waves. - The rainfall in the central Pacific has increased slightly in November but remains considerably lower than that observed in November 1982 and The westerly wind anomaly in the central equatorial Pacific has declined in November. - The general persistence of the southerly winds is probably attenuating the coastal warming. - Most of the climate models predict a decrease of SST anomaly in the Niño 1+2 region between December and March. For these reasons, the ENFEN Committee s increases the estimated likelihood that the Niño coast has a moderate magnitude through March 2016 to 50%, while reducing the likely of strong magnitude to 35% (see Table 1). Even though there is no previous record of a coastal El Niño event with moderate magnitude during the summer, it should be noted that moderate warm conditions may produce heavy rainfall in the northern coast, particularly in the seasonal warmest months (February and March). For the central equatorial Pacific, strong warm condition are expected to persist until January For the southern summer , it is more likely that the central Pacific El Niño will have a strong magnitude (see Table 2). The ENFEN Multisectoral Committee will continue to report on the evolution of the observed conditions and will update monthly the probability estimation of the magnitude in the eastern Pacific (Coastal El Nin o) and in the Central Pacific El Nin o for the austral summer. Multisectoral Committee ENFEN Callao, Peru, December 3 rd, 2015

4 Table 1. Probability of the magnitudes of Coastal El Niño in austral summer (December 2015-March 2016) Magnitudes during December 2015-March 2016 Probability of ocurrence Neutral or Coastal La Niña 5% Weak Coastal El Niño 5% Moderate Coastal El Niño 50% Strong Coastal El Niño (as in ) 35% Extraordinary Coastal El Niño (as in ) 5% Table 2. Probability of the magnitudes of El Niño in the Central Pacific in Austral summer (December 2015-March 2016) Magnitudes during December 2015-March 2016 Probability of occurrence Neutral or Central Pacific La Niña 5% Weak Central Pacific El Niño 5% Moderate Central Pacific El Niño 15% Strong Central Pacific El Niño 50% Very Strong Central Pacific El Niño 25%

5 Figure 1. Time series of SST anomalies in the Niño 3.4 region (a) and Niño 1+2 (b). The black and gray lines indicate the evolution of SST anomalies in the current year information using infrared (IR) and microwave (MW), respectively. The red, blue and green line, indicate the evolution of SST anomalies for 1982, 1997 and 1972.