“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). Most map room issues have been resolved.
The spatial patterns of global SSTs have not changed significantly during the past several weeks. The tropical Indian and west central
Latest TAO buoy data show a steeper than climatology equatorial
Overall, there are many similarities to the SST patterns compared to a year ago. This in itself demonstrates the scientific incompleteness of just using Nino 3.4 to define not only ENSO, but the impacts of global tropical SSTs onto the atmospheric circulation.
http://www.cdc.noaa.gov/forecast1/IndoPacific.frcst.html (note the initial projection)
Tropical convective forcing is still enhanced across portions of the Tropical Northwest Pacific Ocean (TNWP; including Super Typhoon Jangmi approaching
Understanding this spatial pattern of tropical forcing is not trivial, and requires intense daily monitoring within the WB (2007) GSDM framework. An important point to stress is that numerical model performance has decreased substantially over the last few weeks. Subseasonal processes (linking model skill as a function of the WB (2008) measure of the Global Wind Oscillation (GWO) is on the list of efforts for WB to quantify at some point), in addition to seasonal transition, have been responsible. I do feel comfortable with what I think are the on-going global dynamical processes, and will do my best to summarize in the following.
Animations of upper tropospheric daily mean vector wind anomalies show generally zonally oriented chains of midlatitude Rossby wave energy dispersions (RWDs) during the last few weeks. This suggests, and is objectively shown by the real-time WB (2008) measure, that the GWO has been dominating. A major component has consisted of a robust global mountain-frictional torque index cycle during about the last couple weeks (see AAM plots). Around 11 September the global mountain torque involving most north-south massifs was greater then plus 20 Hadleys, followed by a negative event of similar magnitude a few days ago. The frictional torque has loosely been in quadrature. The last occurrence of this type of (weaker) behavior was ~ 1 August (see WB (2008) submitted paper for power spectra).
The point is that the variation discussed above, through processes tied to meridional momentum transports, helped to shift anomalous zonal mean westerly wind flow from the equatorial regions into the midlatitudes. As I type, anomalous easterly wind flow (~3-5 m/s at 200mb) is quickly returning to the equatorial and subtropical atmospheres. Additionally, loosely zonal mean subtropical AAM sinks with poleward source regions have become established in both hemispheres. Finally, updated through 25 September global relative AAM is already at least 1 sigma below the R1 data climatology (without the stratospheric QBO). These are all characteristics of the global circulation trying to return to a La-Nina base state, represented by phase 3 of the GWO 250mb psi snr composite anomaly plot (more said below).
The WB (2008) measure of the GWO and WH (2004) measure of the MJO remain out of sync, the former having a strong projection in octant 8 and the latter in octant 6 of their phase spaces. However, global tropical circulation anomalies are much better represented by the MJO phase 3 250mb psi snr plots, rather than phase 6. For instance, there are upper tropospheric twin tropical anticyclones across the
There is no change in my predictive thoughts from what I typed a week ago. Tropical convective forcing is already festering across the
The current response developing across the PNA sector, shown by the GWO phase 5 250mb psi composite anomaly for the extratropics, is the result of a fast transient RWD forced by the TNWP enhanced convection. I like phases 8-1 of the GWO 250mb psi composites by week 2, meaning some form of troughs coming into to the western states. Afterwards, while GWO variations per above continue, on average (mid-late October?), the phase 3 GWO and MJO 250mb psi and temperature snr composite anomaly plots, typical of a “La-Nina like” low AAM base state, may be most representative. This means a probability shift toward ridging near the west coast and
There are also seasonal cycle issues not addressed in this long discussion. Overall, an enhancement of the weather typical for October appears most likely across the USA during the next few weeks. Per previous postings and above, a rendition of the low AAM base state from 2007-08 may be returning. Synoptically this may mean western and central USA troughs but with added subtropical westerly wind flow. Hence the probability for high impact weather could increase centered on the Plains,
The tropical cyclone risk should hopefully decrease across the TNWP after week-1, while staying at least climatology for the
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.
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 discussion next weekend, ~4-5 October.