El Niño Appears Imminent

[donsutherland1]

The latest data indicates that the onset of an El Niño appears increasingly likely.

Region 3.4 has seen the anomaly average above 0.5°C for July and August. There is little sign that this will change for September.

Region 3.4 Anomalies:
July: +0.61°C
August: +0.83°C
Week of September 1: +0.8°C

The MEI is also continuing to trend upward:
May-June: +0.286
June-July: +0.454
July-August: +0.602

Model data is also generally bullish on the imminent onset of a weak El Niño.

If September sees an anomaly of greater than +0.5°C in Region 3.4, the criteria for an El Niño will be met. The weekly data for the week of September 1 shows an anomaly of +0.8°C.

Also, for what it is worth, the week of September 1 saw a sharp reduction in the cool anomaly in Region 1+2. For August, it averaged -1.18°C. In the week of September 1, it had been sliced to -0.50°C.

As for ENSO Regional anomalies and the PDO, August 2004 saw Region 1+2 have a cool anomaly of greater than -1.00°C and a warm PDO (it rose sharply to +0.85 in August).

Prior to 2004, there were three years that met such criteria in August:

1954
1985
1988

1954 and 1985 saw 2 or more major hurricanes make landfall in the United States. With 2004 having seen one make landfall (Charley) and possibly Ivan making landfall as a major hurricane in the near-future, this is something to think about.

Also, an emerging El Niño does not necessarily suppress tropical activity given the lag between SSTA changes and atmospheric forcing. Hence, one should not rely on the idea that an active hurricane season implies no El Niño in the near future.

Let's take a closer look at two ENSO scenarios (1950-2003) when an El Niño developed during the July-September or October-December periods:

Moderate MEI: less than +0.65 average during hurricane season:

Average named storms: 9.8
Average hurricanes: 6.8
Most named storms: 14
Most hurricanes: 8

If one throws in a weak easterly QBO (above -3) to westerly QBO (>0), then the averages climb to 10.7 named storms and 7.3 hurricanes. The 2004 hurricane season is occurring in the midst of a westerly QBO.

High MEI: at or above +0.65 average during hurricane season:

Average named storms: 6.3
Average hurricanes: 4.0
Most named storms: 7
Most hurricanes: 5

The 1950-2003 averages are 9.9 named storms and 6.0 hurricanes.

The 2004 hurricane season is likely to meet the moderate MEI scenario. Hence, it is more active than what one would likely see if it were a high MEI season ahead of an El Niño.

In any case, the data continue to point to an imminent El Niño.

As an extra note, the 2004 PDO has closely mirrored that of 1977. 1977 also saw a weak El Niño set in, but during the October-December period.

[CaptinCrunch]

Sept. 10, 2004 — NOAA declared today that El Niño is back but this time around in a weaker state. "El Niño conditions have developed in the tropical Pacific and are expected to last through early 2005," said Jim Laver, director of the NOAA Climate Prediction Center. "At this time it is not clear what, if any, impacts this event will have on ocean temperatures in the classical El Niño region along the west coast of South America and on temperature and precipitation in the United States."

Impacts depend on a variety of factors, such as the intensity and extent of the warming in the tropical Pacific. NOAA will continue to monitor the situation in the tropical Pacific and will provide more detailed information on possible impacts due to this event in coming months.

In the release of the El Niño Diagnostic Discussion, the NOAA Climate Prediction Center scientists noted that sea surface temperatures (SSTs) were more than 0.5 degrees C above average in the central and western equatorial Pacific during August 2004. By early September, positive SST departures greater than 0.5 degrees C (~1 degree F) were found between 160 E and 120W, with departures greater than 1 degree C extending from 170 E eastward to 140 W.

"The increase and eastward expansion of warmth in the central equatorial Pacific during July through August indicate the early stages of a warm (El Niño) episode," said Vernon Kousky, NOAA's lead ENSO forecaster. He added, "Through the end of August conditions were not yet indicative of a basin-wide El Niño, particularly due to the presence of below normal sea-surface temperatures in the far eastern equatorial Pacific near the South American coast." The lack of basin-wide warming indicates that this El Niño is likely to be much weaker than the 1997-1998 event.

NOAA declares the onset of El Niño conditions when the three-month average sea-surface temperature departure exceeds 0.5 degrees C in the east-central equatorial Pacific [between 5 degrees -5 degrees S and 170 degrees W-120 degrees W]. To be classified as a full-fledged El Niño episode, these conditions must be satisfied for a period of at least five consecutive three-month seasons.

El Niño is associated with changes in sea surface temperatures in the tropical Pacific Ocean and can have significant impacts on weather around the world. El Niño episodes occur about every four to five years and can last up to 12 to 18 months.

The El Nino/Southern Oscillation (ENSO) Diagnostic Discussion is a consolidated effort of NOAA and its funded institutions. NOAA will continue monitoring El Niño developments and provide monthly updates through its El Niño/Southern Oscillation (ENSO) Diagnostic Discussion. The next update will be issued on October 7, 2004, in association with the U.S. Winter Outlook.