“The views expressed are those of the author and do not necessarily represent those of the National Weather Service.”
Please keep in mind the ESRL/PSD GSDM web link, below, while reading this discussion.
The 91-day signal to noise ratio anomaly composites are now updated daily, centered on the date shown (see product descriptions). Stay tuned as our work slowly moves forward. There have been on-going map room issues causing missing data and unrepresentative plots. Again, this effort is a work in progress with extremely limited resources.
No large changes to the global pattern of SSTs have occurred since my 23 August discussion. The warmest waters (including aerial extent) continue across the Tropical Northwest Pacific Ocean (TNWP) having totals approaching 31C (~1-2C positive anomalies) east of the
An equatorial trade wind surge during July initiated an upwelling oceanic Kelvin wave leading to the negative equatorial subsurface anomalies greater than 3C at roughly 150m depth/150W per TAO buoy data. Another strong trade wind surge (~5m/s 15N-S) is occurring west of the Dateline. Whether or not another upwelling Kelvin wave is generated is unclear. As discussed below, there is some evidence of our low AAM “La-Nina” base state returning.
http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)
Full disk satellite imagery and other tools indicate a strengthening signal of tropical convective forcing centered on the Western Hemisphere and Africa into the
Global relative AAM (updated through 28 August) is a good 1 standard deviation below the R1 data climatology, taking out the westerly phase of stratospheric QBO (not to minimize any importance of the latter). After the respectable clustered (mostly East Asia and Antarctica) positive global mountain torque ~11 August, extratropical Rossby wave trains interacting with tropical forcing and mountains have worked to shift zonal mean easterly wind flow anomalies poleward. That has been particularly true for the northern subtropical atmosphere. Hence a zonal mean AAM sink of ~6 Hadleys has appeared ~40-45N, the largest for the Northern Hemisphere extratropics in at least a couple of months.
Synoptically a Northern Hemisphere response has been a “Branstator (2002) like” circumglobal teleconnection of anomalous midlatitude ridges during the last several days. This was the pattern observed, on average, during the boreal 2007-08 cold season, and is typical of La-Nina (defined globally, not just from Nino 3.4!!!).
While the WB (2008) GWO has been orbiting in phase space from 8-1 to 4-5 with approximately a 10-20 day periodicity, there has been a subtle drift toward octants 8-1-2-3 over the last 90 days. That is consistent with the WH (2004) signal of the MJO shifting ~2 standard deviations in phase space toward the western
The bottom line is I think we have an important weather-climate signal to offer at least reasonable week 1-3 predictions. Whether or not La-Nina returns in some form is unclear, especially since there are endless scenarios I can offer to the contrary. However, this is an example of the serious rigorous daily subseasonal monitoring issues that exist, utilizing the WB (2007) GSDM and WB (2008) GWO frameworks.
Having a bit more confidence than a week ago, rapid global circulation variations given by phases 8-1-2-3 of the 250mb composite anomaly psi from the WB (2008) GWO are most probable weeks 1-3. These will be superimposed upon a slower evolving base state shown by phase 2 and “eventually” phase 3 of the WH (2004) MJO anomalous psi composites, constructively and destructively interfering. The probable
All numerical models have captured an extratropical response consisting of Rossby wave energy dispersing (RWD) from
Obviously extreme weather impacts for the USA week-1 are centered on the landfall of severe tropical cyclone Gustav and possibly tropical cyclone Hanna (and others?) going into weeks 2-3. Please see all official statements from the
More generally, I think it is much too early in the seasonal cycle to “lock in” to a Branstator (2002) circumglobal pattern of anomalous midlatitude ridges (including the central
Intense to severe tropical thunderstorm activity is probable to continue from the central and eastern equatorial Indian Ocean into
Please see the latest official tropical cyclone forecasts for all basins. I trust the expertise of the appropriate meteorological centers to alert the public of additional weather hazards worldwide (high impact weather events are continuing).
Links to CPC and PSD ENSO discussions:
The following is a link to information about the stratosphere and other nice monitoring tools:
The following is a link to NCEP model verifications (surf around for lots more).
The following is a link discussing recent global weather and related events.
These are probabilistic statements. We hope that an opportunity will arise for us (soon) to allow our dedicated web page effort to mature, expediting objectively and accountability. This web page effort will hopefully include an objective predictive scheme for the GWO with hindcasts.
The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, the first of a two-part paper has been submitted to MWR where WB formally introduce the GWO (WB (2008)). A pdf version can be downloaded from the following link:
Overlapping seasonally varying subseasonal composites for variables such as surface temperature, precipitation, geopotential height and streamfunction anomalies are planned on being posted on the web site mentioned above and presented in part-2 of our paper. We want to emphasize notions such as global-zonal mean-regional scale linkages as well as forcing-response-feedback (with subsequent interactions) relationships. An important purpose is to provide a dynamical weather-climate linkage framework to evaluate the numerical models in a sophisticated manner as part of a subseasonal (and any time scale) forecast process, in addition to a climate service for all users. Relying on the numerical models alone is a cookbook!
Given shift work and travel, updates are extremely difficult. I hope to do another discussion next weekend, ~6-7 September.