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The area of SSTs over the
equatorial Pacific that are more than 1 degree C above normal has expanded somewhat in
the most recent week to cover the area between about 160E and 130W, with spots of +1 degree
C anomalies futher east. East of 120W there is an area of essentially near-normal SSTs on
average. Overall, weak El Nino conditions prevail with SSTs in the Nino 3.4 region (120W
to 170W, 5N to 5S) averaging greater than 0.5 C above normal. Below the surface, a warm
pool exists to around 125 meters depth between 160W and 95W. This pool of warmer than normal
water is the result of a Kelvin wave initiated over the western Pacific last summer, that has
moved eastward and shoaled, triggering weak El Nino conditions a few weeks ago. A region of
subnormal temperatures has developed over the western Pacific between 75 and 200 meters depth.
Animated maps of the SST and its anomalies that include the Atlantic show a dramatic cooling
over the western Atlantic and eastern Gulf of Mexico, indicating the large quantities of heat
extracted by the recent anomalously strong hurricane activity in these regions.
The latest
ENSO Diagnostic Discussion dated October 7, 2004 mentions that warm-episode conditions
are expected to continue into early 2005. Positive sea surface temperature anomalies have
increased and expanded during the months of August and September, which indicates the early
stages of a warm episode. In spite of this anomalous warmth, the average pattern of deep
convection has not yet responded along the equator itself. The NOAA operational definition
of an El Nino has been satisfied for the June-September 2004 period. At this time, however,
it is not clear what, if any, impacts on the United States this warm event will have, at
least within the near future.
Mean 200 mb height anomalies for the past 30 days still indicate relatively
cool global tropics and subtropics, although this may be in part an artifact of
the climate normals used. Well below normal heights across western North America
correlates well with unusually cool weather that has prevailed across Alaska and
western Canada throughout most of September, a complete reversal of the temperature
pattern of unseasonably warm weather observed in August and throughout most of the
summer. The persistent anomalous ridge over the northeastern U.S. and southeastern
Canada has helped to keep hurricanes from moving into New England, but has contributed
to an unprecedented onslaught of landfalling hurricanes in Florida. The anomalous
full-latitude trough over the central Atlantic has steered some tropical storms
northward before they reached the Caribbean or North America.
Mean 200 hPa winds and anomalies
show a strong jet stream located across the northern Pacific and southern Canada.
The anticyclonic anomaly center over eastern North America is clearly indicated
and is consistent with recent warmth over that portion of the continent, as well
as the zonally elongated anomalous mid-latitude circulation over the northwest and
north-central Pacific. A weaker anticyclonic circulation is apparent off the coast
of Baja California. An anomalously strong cyclonic circulation is observed over
the western Pacific, centered near 30N.
850 mb winds and anomalies
A broad area of cross-equatorial flow (from the Southern Hemisphere to the Northern
Hemisphere) is indicated over the eastern Pacific from about 120W to the Dateline.
Outgoing Long wave Radiation (OLR), 5-day mean
(Blues imply deep clouds, browns-reds imply few clouds)
indicates areas of suppressed convection over most of the tropical Indian Ocean,
Indonesia, and Australia, but enhanced convection on the Equator from about 140E
to just east of the Dateline, and enhanced convection north of the Equator, along
the Pacific ITCZ near 10N, across much of the Pacific basin. Enhanced convection
over the western Gulf of Mexico and south-central states is associated with
Tropical Storm Matthew.
Observations and forecast of principal storm tracks and 700mb storm activity (shading)
shows that it has been generally quite stormy over much of the middle latitudes of
the Northern Hemisphere that past two weeks, and a similar pattern of storminess
is forecast for the next week.
Shading on this latter figure
is the MAXIMUM of the absolute value of the difference between the v- (north-south) component
of the wind, and the 7-day average, V, of v, i.e., |v'| = max|(v - V)|,
at 00 and 12 UTC for the seven-day period indicated to the right of the figure when
|v'| was at least 12 m/s. The boundary between no shading and the
lightest color marks the first shaded contour, which represents 12 m/s, the
second contour is 16 m/s, the third is 20 m/s, etc...
MJO monitoring tools show upper level divergence moving toward the Dateline,
which would be favorable for enhanced convection there. Increased subsidence and
suppressed convection has moved to be centered over 60E.
MJO prediction tools (CPC) The EWP model predicts the areas of suppressed/enhanced
convection to move slowly eastward over the next few weeks. The convection over the
"maritime continent" region (Indonesia/Malaysia sector) is forecast to become even
more suppressed. Pacific convection (max along the ITCZ near 10N latitude) is expected
to shift east with time, while suppressed convection appears poised to expand eastward
from northern South America toward western Africa but weaken.
MJO prediction tools from NOAA's Climate Diagnostic Center
the NCEP ensemble forecast agrees that the area of upper-level convergence and
suppressed convection over the western Pacific will move toward the central
Equatorial Pacific over the next two weeks, while the CDC ensemble forecast
takes this area and expands it to cover much of the Indian Ocean as well as
the "maritime continent" region, but does not move it appreciably eastward.
The Wheeler forecast moves the initial pattern only slightly eastward.
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