I want to use this posting as a “precedent” to shortening (still need to work on that!) these discussions given time issues. Interested readers should know where to look on the web to examine details such as, for example, SSTs. There may also be “obvious features” and issues that will be skipped over.
Basin wide (within 5 deg of the equator) moderate La-Nina SST anomalies remain having magnitudes colder than minus 2C near the equator at ~125W per TAO buoy data. The west central Pacific Ocean still has totals in excess of 30C along the equator at 140E slowly shifting south with the annual cycle. Weak warm anomalies remain across the Indian Ocean while the Atlantic basin is still warmer than climatology.
Even though it is probable for this moderate cold event to persist at least through December 2007, I am unclear afterwards. Understanding the seasonal cycle, there is actually weak subsurface warming occurring to at least 150W with anomalies ~plus 1C/150m. This may be a response to equatorial westerly wind events in the region of Indonesia to the date line late September and again about 10 days ago (anybody want to call this an oceanic Kelvin wave?). Trades are again intensifying around the date line in response to tropical convective forcing increasing back to the west. Stay tuned.
Satellite imagery and other diagnostic monitoring tools do give a signal of tropical convective forcing intensifying and organizing in the region the equatorial central Indian Ocean into northern Indonesia. Per animations of upper tropospheric velocity potential fields, the Western Hemisphere dynamical signal is propagating into Africa and the Indian Ocean, enhancing tropical forcing across those regions. The latter was forced by interactions with the extratropics.
Animations of upper tropospheric daily mean vector wind anomalies present an improving signal of twin tropical/subtropical anticyclones ~60-100E with cyclones near 170E. In fact, equatorial westerly wind anomalies having magnitudes ~25m/s have responded over the Western Hemisphere Pacific Ocean. Finally, there are lower level twin cyclonic circulation anomalies ~60-90E which may develop into tropical cyclones. In any case, at least a weak MJO may be in the early stages of formation given the baroclinic structure. The WH (2004) RMM phase space plots present ~1 standard deviation MJO signal across the Eastern Hemisphere with no clear sense of what it will do. My own feeling is we will see at least a truncated weak MJO during the next few weeks, having eastward propagation to ~140-150E where tropical SSTs are the warmest. This may be similar to what happened late September, except that situation not a “true” MJO.
Through 24 October, global relative AAM has dipped to ~minus 2.5-3 standard deviations (approximately AMUs) below the R1 data climatology, after our positive global mountain torque (mostly East Asian; ~25 Hadleys) roughly 10-14 days ago. The Global Wind Oscillation (GWO) which takes into consideration non-oscillatory extratropical dynamics linked to the surface torques and AAM transports, has orbited to ~minus 1.5-2 standard deviations into the phase plane of GSDM Stage 4-1 through 22 October. Zonal mean easterly wind flow anomalies (~5-10m/s at 200mb) have re-intensified throughout the global subtropics. In summary, ocean-atmosphere coupling to La-Nina appears to be once again strengthening, including a poleward AAM transport signal, with perhaps a MJO perturbation.
For the PNA sector, predictability has been VERY LOW for both myself and the numerical models during the last couple weeks. In retrospect, speculation suggests a mountain torque enhanced North Pacific jet (which we had) collapsing in a base state favoring anticyclonic wave breaking (AWB) may not be very predictable even at "short" lead times in regard to synoptic details, particularly during boreal fall. In fact, the above sequence of events greatly contributed to the severity of the wild fires across California. I do think a “classic” GSDM Stage 1 cold season response meaning tilting the odds toward an anomalous western USA trough (with synoptic variations) is in the near future. In the meantime, seasonal strengthening of the westerlies has finally led to a relatively tranquil weather pattern across much of the USA.
Going into week 2, I do have a concern the trough that most models suggest to come into the western USA will be slower and deeper, with even another one of those __________ AWB closed lows. In fact, these kinds of synoptic situations may be probable this cold season, as the southwest flow storm track presumably becomes established across the central states.
Please see the latest statements from the NOAA/NWS/Tropical Prediction Center for tropical cyclone statements. There is evidence at this time a tropical depression may be forming across the southeast Caribbean. Locations including the Arabian Sea, Bay of Bengal and even the South Indian Ocean may need to deal with at least 1 tropical cyclone week 1. The Northwest Pacific Ocean around the Philippines may be a concern for tropical cyclone development through at least week 2. While dryness returns to tropical South America for at least week 1, portions of equatorial Africa may remain quite wet. Will there be another “Gabrielle” across the North Atlantic Ocean sometime soon?
Appendix
An experimental quasi-phase space plot of the GSDM utilizing a time series of normalized relative AAM tendency anomaly (Y-axis) and normalized relative AAM anomaly time series (X-axis) can be found at
http://www.cdc.noaa.gov/map/images/gcm/gsdm_95d.jpg
http://www.cdc.noaa.gov/map/images/gcm/gsdm_40d.jpg
http://www.cdc.noaa.gov/map/clim/gsdm.shtml
We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the GSDM is to extend current thinking beyond the MJO, the purpose of the GWO is to illustrate the non-oscillatory stochastically forced component of the GSDM.
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/
These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. I will try to post another discussion late next week ~ 2-4 November before travel the following week.
Ed Berry
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