What goes around...or does it?

“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.

http://www.cdc.noaa.gov/map/clim/gsdm.composites.shtml

The composites are still centered on 1 July, and work is on-going to update them regularly. Stay tuned. Again, this effort is a work in progress with extremely limited resources.

The following are links to global SST information. Weak warm SST anomalies (~0.5C per TAO buoy data) continue from the west coast of South America into the equatorial East Pacific Ocean. Surface westerly wind anomalies partially forced by the extratropics has persisted these positive SST anomalies. However, these anomalies are not very deep. Having my reasons, I think a significant equatorial Pacific Ocean basin wide warm event (El-Nino) is unlikely during the upcoming 2008-09 boreal cold season.

http://www.wmo.int/pages/prog/wcp/wcasp/enso_update_latest.html

http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html

http://www.pmel.noaa.gov/tao/jsdisplay/

http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/index.primjo.html (link 18)

http://www.cdc.noaa.gov/map/images/sst/sst.long.time.gif

As was offered on my 23 July posting, Eastern Hemisphere tropical convective forcing has been slowly propagating east-northeast toward the northwest Pacific Ocean (~5-6m/s phase speed). Full disk satellite imagery shows this enhanced rainfall extending from India east-southeast to north of New Guinea, centered on approximately the Philippines. Forced by the Southern Hemisphere extratropics, separate flare-ups continue over the western equatorial Indian Ocean. The latter has been a recurring feature since at least early June. WH (2004) MJO plots through 31 July indicate a slightly less than 1 sigma projection in octant 4 of phase space (w/wo interannual component), having little eastward movement during the last few days (more said below).

During the last half of July dynamical processes tied to the tropical convection and the extratropics worked to add global westerly wind flow. In fact, relative AAM peaked just above the R1 data climatology ~30 July. Anomalous zonal mean westerly wind flow was generated in the northern equatorial atmosphere around mid-July, only to propagate poleward and downward since. The latter has been in the presence of other midlatitude zonal bands of anomalous westerly wind flow. Particularly in the austral winter Southern Hemisphere storm track regions, frictional dissipation of this westerly wind flow has been occurring over the last couple of weeks. In fact, the zonal mean frictional torque anomaly around 25S has been minus 2 Hadleys and lower.

Continuing, my point is that I think once again westerly wind flow is decreasing globally. For example, Rossby wave energy dispersions (RWDs) tied to the Eastern Hemisphere tropical convective forcing arcing across the South Pacific Ocean is contributing to a strong negative Andes mountain torque. That along with other complicated dynamical processes (to save space!) has forced the global relative AAM tendency to roughly minus 20 Hadleys allowing the WB (2008) GWO to orbit solidly into octant 8-1 of phase space (averaging period issues understood).

One bottom line for predictive purposes is that I do expect a signal having a MJO component to propagate through the Western Hemisphere during the next few weeks. Most statistical and dynamical MJO forecasts utilizing the WH (2004) methodology do not support this notion very well.

However, I think it is less likely there will be the strong enhancement around the Americas as observed ~mid June-mid July. In addition to dynamical forcing from extratropical RWDs, I think the latter may have involved some constructive interference between an equatorial Atlantic convectively coupled Rossby mode and the previous MJO. The Rossby mode may have been a response to what was persistent tropical convective forcing across the eastern equatorial Atlantic Ocean during boreal late winter-spring. Above average SSTs, perhaps due to an "Atlantic El-Nino", contributed to that enhanced convection.

Another bottom line is that the quasi-stationary component to our global circulation base state favoring a low AAM regime has not completely gone away. The recurring convective flare-ups over the western equatorial Indian Ocean per above is a manifestation of this. Hence I do think the WB (2008) GWO is probable to loosely orbit tilted toward phase 3 (La-Nina base state) “until further notice”. In fact, I remain concerned some reprisal of the “2007-08 season of the witch” may occur this upcoming boreal cold season.

On my 23 July discussion I suggested with low confidence a “pattern shift of sorts” across the USA may occur favoring a ridge around the west coast and a trough in the middle of the country going into this month. None of the numerical models or official predictions suggested this. Latest model runs now favor a situation similar to this regional scale response for next week. Hence the intense heat that is about to expand eastward across the central and eastern states is probable to last only a few days.

However, my feelings for success of this subseasonal prediction are limited and mixed. I was favoring a stationary pattern given by phases 3-4 of the GWO 250mb psi and temperature anomaly composites. Instead, a relatively large orbit in GWO phase space occurred.

For weeks 1-3, interestingly enough, with variations understood, phases 3-4 and 4-5 of the GWO anomaly composites (250mb psi and temperature) along with MJO temperature anomaly phases 4 and 5 appear to be the most probable outcome for the country. Again, these are composite signals and need to be updated. Also, given recent relatively weak weather-climate signals and a tendency for “fading in and out (not discussed)”, my confidence remains low.

As the Plains cool down next week, intense MCS activity may shift southward impacting locations from eastern Colorado-Wyoming into at least Iowa and Missouri. The MCS storm track is probable to shift back to the northeast as intense heat may return to the Central and Southern Plains weeks 2-3. Other locations possibly impacted by periods of heavy rainfall and severe local storms are portions of the eastern states weeks 1-3.

Intense to severe tropical thunderstorm activity should shift east and north through portions of India, Southeast Asia and the northwest Pacific Ocean during the next 1-2 weeks. Locations that may be hardest hit include the South China Sea and the Philippines into the west central Pacific Ocean. Going along will be the risk of tropical cyclone development. Persistent tropical forcing is also likely across the western equatorial Indian Ocean. During weeks 2-3, while tropical thunderstorm activity may weaken slightly across the Eastern Hemisphere, some enhancement is likely over the Americas. The risk of tropical cyclones may increase across the East Pacific Ocean week-2 and Atlantic by week-3 (above climatology).

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.

Appendix

Links to CPC and PSD ENSO discussions:

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml

http://www.cdc.noaa.gov/people/klaus.wolter/MEI/

The following is a link to information about the stratosphere and other nice monitoring tools:

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/index.html

The following is a link to NCEP model verifications (surf around for lots more).

http://www.cpc.ncep.noaa.gov/schemm/z500ac_wk2_na.html

The following is a link discussing recent global weather and related events.

http://www.wmo.ch/pages/mediacentre/news/index_en.html

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. A pdf version can be downloaded from the following link

http://www.cdc.noaa.gov/map/clim/wb08_final.pdf

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 late next week.

Ed Berry