Saturday, September 20, 2008

Short Update

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 (snr) anomaly composites are now updated daily, centered on the date shown (see product descriptions). On-going map room issues causing missing data and unrepresentative plots are getting resolved.

There is little change in the global tropical SSTs from a week ago. Perhaps most notable is the warming of the equatorial and South Indian Ocean with totals in excess of 29C and anomalies ~plus 2C. See links below. (note the initial projection) (link 18).

Decoupling of signals defined by the WH (2004) measure of the MJO and WB (2008) measure of the GWO has occurred. Interactions between tropical convective forcing shifting into the TNWP, extratropical processes involving the eddies and global mountains have removed subtropical easterly wind flow anomalies. Through 18 September global relative AAM was near the R1 data climatology.

A recent strong positive global mountain torque event, ~20 Hadleys largely from the Andes, has forced the WB (2008) GWO signal to propagate rapidly through the Western Hemisphere. In fact, the zonally oriented RWDs, characteristic of the GWO, led to a rapid increase of tropical convection around the Americas this past week. Through 18 September the GWO was in octant 8 of phase space, and the corresponding snr composite anomalies of air temperature and 250mb psi are representative for North America.

Meanwhile, the weakening WH (2004) MJO signal was in octants 5-6 of phase space (~1 sigma projection). However, leaving the interannual component in, the projection was much weaker and drifting toward Phase 3. Hence phase 3 of the MJO 250mb psi and 2m air temperature composites may best represent current tropical circulation and North American 2m air temperature anomalies, respectively.

During the next several weeks (exact timing is noise), the WB (2008) GWO should continue ~10-20 day orbits in phase space, from octants 8-1 to 4-5. I expect the GWO signal mentioned above, already coming back into the Eastern Hemisphere, to contribute to a rapid increase of equatorial Indian Ocean tropical convection by roughly the end of week-2. I also think the tropics and extratropics are probable to sync up once again. The WH (2004) MJO signal should shift back into octants 3-4 of phase space. While stochastic processes maintain the 10-20 day GWO orbits, a drift toward “the low AAM portion (La-Nina like) of GWO phase space” may also occur.

For North America, I like phases 8-1 of the GWO snr composite anomaly 250mb psi and 2m air temperature depictions for week-1, then plots 4-5 for ~week-2. Synoptically this translates to a North Pacific Ocean jet extension after next week leading to ridging across the western USA. A return to phases 8-1 is possible weeks 3-4, but perhaps with troughs extending farther south across the western and central portions of the country. Weather ramifications should be understood. There is no change in my thinking going into boreal winter.

Tropical cyclone risks will continue from the TNWP into the Western Hemisphere basins weeks 1-2. In fact, the tropical cyclone risk may be greatest from the Gulf of Mexico and Caribbean into the Atlantic Ocean weeks 2-3. Intense to severe thunderstorm activity is probable to increase from equatorial Africa into the Indian Ocean the next 1-2 weeks, with convection shifting east-northeast into India and the Maritime Continent afterward. The risk of Arabian Sea and Bay of Bengal tropical cyclones may increase by weeks 2-4.

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 still 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, where WB formally introduce the GWO (WB (2008)), has been accepted for publication in MWR. The authors are in the process of resubmitting after a minor revision. A pdf version (before revision) 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! I should be able to do a complete discussion next weekend, ~27-28 September.

Ed Berry

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