Atmospheric Insights

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

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).

Full disk satellite imagery and other tools indicate a strengthening signal of tropical convective forcing centered on the Western Hemisphere and Africa into the Indian Ocean. With the all important interannual component left in, since about 6 August there has been ~2 sigma MJO projection in octant 2 of WH (2004) phase space. Phase 2 of the MJO 250mb psi composite anomaly represents the current tropical circulation anomalies, including a favorable environment for Atlantic Ocean tropical cyclogenesis. Some eastward propagation of this MJO signal has occurred during the last week or so. In fact, tropical convection has been moving east along the equator across Indonesia at ~7m/s. However, having my reasons, I am suspicious the latter is only a transient component within a generally quasi-stationary situation of (extremely complicated) tropical forcing.

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 Indian Ocean during this same period. The latter suggests a resumption of tropical-extratropical coupling favoring a return to a La-Nina global circulation.

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 USA temperature outcomes can be seen from the corresponding temperature composite anomaly plots, as well as the tropical convection from the composite OLRA plots.

All numerical models have captured an extratropical response consisting of Rossby wave energy dispersing (RWD) from Indian Ocean tropical forcing. Consistent with phase 1 of the WB (2008) GWO 250mb psi composite anomaly plot, western USA troughs are probable week-1. As shown by the GWO phase 2-3 composites, ridging may return to the west coast while troughs amplify across the central states ~weeks 2-3. I would be very careful with the predicted synoptic details of any ensemble numerical model after especially day 5 in this weather-climate regime.

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 Tropical Prediction Center. I think the North Tropical Atlantic Ocean will remain favorable for additional cyclone development through at least week-2 (above climatology). Substantial precipitation is likely from the Rockies into the Plains and Mississippi Valley week-1, shifting eastward weeks 2-3. I think the notion of some model forecasts to drift the remains of Gustav as far north as Iowa late next week are not unreasonable.

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 North Pacific Ocean). However, should it become clear that a rendition of a low AAM base state may persist through boreal winter 2008-09, anomalous western and central USA troughs may be probable starting around November-December. These may have an Arctic cold air source to work with, along with more subtropical westerly wind flow, latter compared to last winter.

Intense to severe tropical thunderstorm activity is probable to continue from the central and eastern equatorial Indian Ocean into Indonesia and the monsoon systems week-1. Unlike the past 2 subseasonal events, this area of rainfall is probable to stay farther south, consistent with the seasonal cycle. How far east the enhanced tropical convection coherently moves is unclear. However, a transient component impacting the west central and TNWP is a possibility anytime until further notice, including at least hybrid tropical cyclones. There may be a reduced risk for significant East Pacific Ocean tropical cyclone development at least week-1, while the tropical Americas have generally climatology for rainfall. Finally equatorial Africa is likely to remain wet with intense easterly wave activity at least weeks 1-2.

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).

Appendix

Links to CPC and PSD ENSO discussions:

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

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

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).

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 (WB (2008)). A pdf version can be downloaded from the following link:

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

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.

Ed Berry

Saturday, August 23, 2008

Ressurecting the Atmosphere from the Noise

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. Again, this effort is a work in progress with extremely limited resources.

Global tropical SSTs continue to exhibit spatial patterns that cannot be summarized by relatively trivial indices such as Nino 3.4, IOD, PDO (which also considers the extratropical North Pacific Ocean), etc. Anomalous warmth (~1-3C) broadly exists in locations such as the equatorial Indian Ocean, west central and northwest Pacific Ocean, equatorial east Pacific and finally the areas of the Caribbean into the Atlantic Ocean. Cool anomalies of similar magnitude are present around Indonesia and the equatorial Dateline. The warmest SSTs globally (totals ~30C) having the largest areal extent are still across the Tropical Northwest Pacific Ocean (TNWP).

It is not the point of these discussions to offer SST attribution (see links below). However, the above summary is given to emphasize that atmospheric responses to global tropical oceans constantly impact locations such as the USA. Statements such as “ENSO neutral” are extremely misleading, and not scientifically complete. In fact, weather-climate linkage signals involving the global tropical SSTs may be rising out of the noise as I type.

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

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

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

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)

I want to follow-up from the 15 August posting. The weather-climate situation remains tremendously complicated and difficult to write about in a focused manner. However, for the first time in at least the past 1-2 months, tropical convective forcing has been slowly intensifying farther east across the anomalously warm equatorial Indian Ocean during the last week. Per full disk satellite imagery this region of enhanced tropical rainfall is located ~60-100E, having 3-day OLRA ~minus 30-50W/m**2. Other pockets of enhancement remain across the TNWP and the Americas.

Regardless of all the “wandering” details, there is evidence that a subseasonal event is developing, including a MJO component. WH (2004) plots updated through 21 August show a significant projection of ~1.5 sigma in octant 2 of phase space. Leaving the interannual component in, the projection is roughly 2 standard deviations in octant 2, not trivial. The phase 2 MJO streamfunction (psi) composite anomaly per GSDM web link strongly represents the global tropical wind circulation. Repeating from a week ago, there has been a decided shift toward Indian Ocean tropical forcing in WH (2004) phase space. As pointed out by Weickmann of the WB (2008) GWO, the MJO projection, a component to the GWO, is increasing as the interannual portion slowly weakens.

To fully appreciate the recent behaviors to the WB (2008) GWO, in addition to carefully understanding some of the dynamical principles discussed in our submitted paper, rigorous daily monitoring has been critical. Loosely, faster time scale processes due to midlatitude mountains and baroclinic eddy Rossby wave energy dispersions (RWDs) have contributed to ~10-20 day orbits in GWO phase space (recall 15 August posting). These circuits have been from octants 4-5 to 8-1, with a “drift” toward low AAM.

Taking out the westerly QBO phase of the stratosphere, updated through 21 August global relative AAM has dipped to ~1.5 standard deviations below the R1 data climatology. Not only has anomalous zonal mean easterly wind flow (~5-10m/s at 200mb) returned to the tropical and subtropical atmospheres, there is evidence of poleward propagation. Furthermore, anomalous zonal mean westerly wind flow on the poleward flanks of these easterlies has brought back our familiar pattern strong midlatitude ridges, including the central North and South Pacific Oceans.

So, lets try to put all the above together. It is too early and uncertain for me to say subseasonal tropical-extratropical coupling involving the MJO and GWO is starting. However, even though the time scale is unclear, my suspicion is yes (per above), and stay tuned. A few of the serious subseasonal monitoring issues include: 1) if we are starting some rejuvenation of our low AAM base state similar to the boreal 2007-08 cold season, 2) if we are seeing the first of several coupled subseasonal events that may eventually shift into the anomalously warm west central Pacific Ocean, perhaps initiating a warm event (El-Nino), and 3) the weather-climate situation remains in a sea of noise. Whatever happens, there will be upcoming high impact weather globally, and stating “ENSO neutral” does not “cut it”.

Until I get impressed, my card will be to stick with the notion of a weakly low AAM base state having superimposed rapid GWO variations. Unlike my previous discussion, however, I do want to take into consideration the possibility of a subseasonal event for week 1-3 predictions, which includes an east-northeast shift of the Indian Ocean tropical convective forcing.

For weeks 1-3, rapid global circulation variations given by phases 4-5 and 8-1 of the 250mb composite anomaly psi from the WB (2008) GWO are most probable. These will be superimposed upon a slower evolving base state shown by phase 2 and eventually phases 3-4 of the WH (2004) MJO anomalous psi composites, constructively and destructively interfering. The probable USA temperature outcomes can be seen from the corresponding temperature composite anomaly plots, as well as the tropical convection from the composite OLRA plots. Obviously this is a very low confidence outlook.

Numerical model solutions for the USA have been inconsistent and varied for the next 1-2 weeks. Not only will model performance suffer going into boreal autumn, the weather-climate situation discussed above will also contribute (another item on list of work for WB to show). Broadly, the barrage of troughs digging into the Rockies and Plains then shifting east has started. Individual synoptic details beyond ~day 3 in this type of circulation regime are white noise, and attempts to predict them (for the public) is a waste of resources as well as scientifically indefensible. Skill is derived from statements of probability.

Should an eastward shifting subseasonal event including the MJO component occur, a more persistent and deeper western USA trough shown by MJO psi composite anomaly phase 4 may occur late week-2 into week-3. In addition to intense/severe precipitation including thunderstorms for the central USA, early season heavy snow may occur for portions of the northern Rockies during the ~second-third weeks of September. Reiterating from my previous discussion, western and central USA troughs with subtropical westerly wind flow may be the most likely outcome going into boreal winter (having my reasons).

Intense to severe tropical thunderstorm activity is probable continue across the equatorial Indian Ocean week-1 shifting east and north into the Indian and Asian monsoon systems while also impacting portions Indonesia by week-2. It is not out of the realm of possibilities for this intense thunderstorm activity to impact the TNWP by week-3. Regardless, the west central and northwest Pacific Ocean will be a wild card for numerous reasons until further notice, including the risk of tropical cyclones. The tropical Americas and North Atlantic Ocean appear to remain anomalously active week-1 and likely into week-2.

Appendix

Links to CPC and PSD ENSO discussions:

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

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

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).

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

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/gsdm.composites.shtml

Given shift work and travel, updates are extremely difficult. I hope to do another discussion next weekend, ~30-31 August.

Ed Berry

Friday, August 15, 2008

The Mess

“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.

There is little significant change to the global pattern of SSTs discussed a week ago. The warmest ocean waters are from the west central into the tropical northwest Pacific (totals ~29-30C), and anomalous warmth persists across the equatorial Indian Ocean. The positive SST anomalies east of 140W along the equatorial Pacific Ocean have increased to at least 1-3C, but with totals less than 27C. The latter anomalies are not trivial and are a significant concern for possible impacts on the inter-yearly component of global ocean-atmospheric variability, remembering seasonal cycle and interannual issues. See links below.

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

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

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

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)

The weather-climate situation is extremely complicated having mixed signals. Many different interpretations can be offered. Regardless, this is another example where “cookbook prediction techniques (including relying on the models alone)” and blanket statements like “ENSO neutral” are not scientifically complete efforts. I want to do my best to cut to the chase what rigorous daily monitoring within the WB (2008) GWO and WB (2007) GSDM frameworks are telling me.

Enhanced tropical convective forcing is concentrated in the region of India to Southeast Asia (~15-30N; shifted anomalously north similar to a year ago), the west central Pacific Ocean and around the Americas. The flare-ups continue across the west central equatorial Indian Ocean. Through 14 August WH (2004) phase space plots show a stationary projection of roughly 1 sigma in octants 1-2, and nearly 1.5 standard deviations in octant 2 leaving the very important interannual base state in. In fact, there has been a decided interannual shift toward the Indian Ocean during the last few months. Among other arguments, I think dynamical processes linked to our past low AAM base state (2007-08) are contributing to the west central equatorial Indian Ocean flare-ups.

Even though the WH (2004) plots show a projection in ~octant 2 in phase space, in reality some of the recent Western Hemisphere enhancement can be attributed to the July MJO event. In addition, driven largely by positive global mountain torques, particularly the East Asian component, there have been two recent ~10-20 day fast orbits in the WB (2008) GWO phase space. Specifically, ~6 August both the East Asian and global mountain torques were roughly plus 15 Hadleys (R1 data), with the former having an approximately 10-day periodicity. Through 13 August the torques remain positive, with a tendency for North America and East Asia to remain out of phase (an old base state issue). Broadly, the GWO orbits have involved phases 8-1 to 4-5.

The bottom line is I think extratropical Rossby wave energy dispersions (RWDs) involved with the fast GWO orbits contributed to both the Western Hemisphere signal (in addition to the MJO) and the west central Pacific Ocean tropical convection. AAM transports tied to the mountain torques have “helped” to shift zonal mean westerly wind flow anomalies off the equator to well into the subtropical atmospheres (~30N/20S). An extratropical PNA response has been an anomalous extension of the polar jet stream across the North Pacific Ocean (~45N/250mb wind speed anomalies roughly 30m/s) leading to west coast ridge amplification and a trough in the central USA. The latter is consistent with phase 4 of the GWO composite, and that was the location in phase space of the GWO ~7-9 August.

Zonal mean easterly wind flow anomalies are increasing across the global tropics, and phase 2 of the WH (2004) MJO composite streamfunction anomaly represents the tropics very well. During approximately next week, temperature composites on phases 8-1 of the WB (2008) GWO are reasonable, suggesting a western USA trough (models have caught this). I do think it is probable for the GWO and MJO locations in phase space to sync up during weeks 2-3, favoring octants 2-3. The attendant dynamical processes will drive global AAM to be below normal. I also suspect there will be a coherent eastward shift of this coupled tropical-extratropical forcing, possibly into the west central and northwest Pacific Ocean. The temperature and streamfunction anomalies shown by GWO/MJO composite phases 3-5 may be most representative for North America during weeks 3-4.

Finally, a serious subseasonal monitoring issue will be to see not only far east the above mentioned coupled forcing shifts, but also for subsequent events. Should strong tropical convective forcing initiate equatorial westerly wind bursts across the anomalously warm west central Pacific Ocean (and oceanic Kelvin waves), a change in the interannual base state may evolve. Until then (if at all), I favor a tilt toward a weakly low AAM base state having important subseasonal events. Having my reasons, the barrage of troughs into the western and central USA may resume boreal fall going into winter, but with additional subtropical westerly wind flow.

The solutions being served up by most models are reasonable through days 7-10. Among other impacts (should be understood), intense/severe MCS activity may return to the Northern Plains and Upper Mississippi Valley week-2. As suggested by the GSDM composites, troughs would then be more probable to deepen into the central states then shift east particularly weeks 3-4. The global circulation regime appears quite favorable for Atlantic Ocean tropical cyclogenesis for at least the next 1-2 weeks (already have Tropical Storm Fay).

Intense to severe tropical thunderstorm activity is probable to persist and even intensify across the Eastern Hemisphere monsoon systems of India and Southeast Asia through at least weeks 2-3. There will be the seasonal southward shift of this activity going into boreal autumn. The west central and northwest Pacific Ocean will be a wild card for numerous reasons until further notice, including the risk of tropical cyclones. Hopefully there will some Western Hemisphere suppression later week-2 and week-3.

Appendix

Links to CPC and PSD ENSO discussions:

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

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

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)

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

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/gsdm.composites.shtml

Given shift work and travel, updates are extremely difficult. I hope to do another discussion next weekend, ~23-24 August.

Ed Berry

Thursday, August 07, 2008

The Day the Atmosphere "Stood Still" ???

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 90-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. Again, this effort is a work in progress with extremely limited resources.

The warmest SSTs globally are centered on the tropical northwest Pacific Ocean ~10-20N/150E having totals ~29-30C. The anomalous warm and cool horseshoes of SSTs remain across the Pacific Ocean basin, along with the positive anomalies across the equatorial east Pacific. Broadly similar to the last 2 boreal summers, a positive-negative-positive anomaly spatial SST pattern is present from the Indian Ocean to the west central Pacific Ocean. SSTs across much of the tropical Atlantic Ocean basin are well above climatology.

The general consensus in regard to the interannual component is “ENSO neutral”. Regardless of “labeling”, constant evolutionary dynamical processes involving all components of the weather-climate system continue. These include complex subseasonal processes, and will contribute to additional high impact weather globally. I do remain concerned that a renewed tilt toward a low AAM base state (a “weakened rendition” of the 2007-08 La-Nina) is the most probable outcome for at least the next 3-6 months (more said below). See the following links for SST details.

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

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

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

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)

Eastern Hemisphere enhanced tropical convective forcing has shifted well north, extending from approximately northern India/Pakistan (where flooding deaths have occurred) through southeast China into the northwest Pacific Ocean. The core of this activity is at ~15-20N/120E, with recent 3-day averaged OLRA less than minus 90 W/m**2 per BMRC. Tied to the Southern Hemisphere extratropics, flare-ups continue over the anomalously warm west central equatorial Indian Ocean. There has also been an increase of tropical convection along Pacific Ocean ITCZ as well as the Americas during the last few days.

WH (2004) MJO plots updated through 6 August, while showing a slightly less than 1 sigma projection in octant 2 of phase space without the base state left in, present a somewhat greater than 1 standard deviation signal with the interannual component. As was suggested by many MJO predictions in WH (2004) phase space at least a week ago, a westward shift of this tropical signal has occurred. I think much of the signal has come from the winds (tied to the processes explained by WB (2008) GWO).

In any case, not only must users carefully understand the derivation of the empirical WH (2004) technique and related predictive tools, but much more importantly the dynamics responsible for the recent behavior of this tropical forcing. The bottom line is I think coupling between the tropics and extratropics is still present meaning the now familiar low AAM quasi-stationary component to the global weather-climate situation may be (again) starting to dominate. Going into the boreal cold season, subseasonal processes may change this.

The enhancement across the Western Hemisphere can be attributed to faster processes such as convectively coupled Kelvin waves (per coherent modes Hovmollers) and those linked with the WB (2008) GWO. I do have more confidence relative to my 1 August posting this Western Hemisphere signal of enhanced tropical forcing will not be as robust as ~late May and early July.

Through 5 August global relative AAM (including the westerly phase of the stratospheric QBO) was slightly below the R1 data climatology with its computed tendency ~minus 10 Hadleys forcing the WB (2008) GWO to roughly octant 8-1 of phase space. Since approximately 20 July a relatively fast orbit has been occurring. One contributor has been the global mountain torque, with the positive East Asian component (~10 Hadleys) out of phase with the global signal. The latter is very complicated (but explainable), and has been a characteristic feature of our low AAM base state for the past several months. Regardless, I think the current Western Hemisphere tropical convective signal is partly a response to this fast WB (2008) GWO. The trough that most models predict to impact the USA during roughly days 4-7 is also a response to the fast WB (2008) GWO including the positive East Asian mountain torque.

Zonal mean westerly wind flow anomalies (~5m/s at 200mb) have shifted off the equator to roughly 15N, while 5-10m/s anomalous zonal mean easterly wind flow anomalies persist in the subtropical atmospheres. In fact, anomalous midlatitude ridges are again present across the global midlatitudes, having a zonally oriented character across the Northern Hemisphere. The latter is characteristic of a Branstator (2002) circumglobal teleconnection (and is also connected to the recent negative NAO phase – red noise!!!), as observed frequently during the boreal 2007-08 cold season.

Specifically, everything considered (this discussion is already too long!!!), WB (2008) GWO and WH (2004) MJO phase 3 streamfunction (psi) and 2m air temperature anomaly composites best describe the current global weather-climate situation. Animations of upper tropospheric daily mean vector wind anomalies show twin anticyclones becoming better defined in the region of Africa/Indian Ocean with downstream twin cyclones. This supports the notion of a low AAM quasi-stationary regime, as well as the composites I am “pointing to”.

Weeks 1-3 across the USA should see synoptic events featuring troughs digging into the middle of the country, then moving to the East Coast. Ridging is most probable in the region of the west coast. I think the 2m air temperature anomaly pattern given by WB (2008) GWO phase 3 may be the most representative, on average. However, there will be orbits in phase space, and keep in mind other GWO/MJO composites such as phases 2 and 4. Phases 5-7 are the least likely. Similar to the last few days, intense rainfall and MCS activity (including severe local storms) will continue to periodically impact much of the central and eastern portions of the country. I think the latest official week-2 forecast is too dry for much of the middle USA, especially the Upper Mississippi Valley and particularly around Iowa. The increasing subtropical westerly wind flow mentioned above supports wetness from the Desert Southwest into the Plains.

Should this low AAM quasi stationary component (key word) of the global circulation regime persist well into the boreal 2008-09 cold season, outcomes of USA temperature and precipitation anomalies having some similarity to 2007-08 are again possible. The barrage of western USA troughs may resume. One difference may be for wetness to expand farther south into the Plains given what may be increased subtropical westerly wind flow (I have my reasons).

Intense to severe tropical thunderstorm activity should increase across the equatorial Indian Ocean during the next 1-3 weeks while expanding northeast into the monsoon and frontal band systems. Given the very warm SSTs, the tropical northwest Pacific Ocean is likely to remain periodically active, including an elevated risk of tropical cyclones. In fact, both the Indian and west Pacific Oceans may be anomalously convectively active going into boreal autumn. Stay tuned to see if our "old nemesis of the new world atmosphere" returns. The central and east Pacific Oceans will have a tropical cyclone risk at least week 1, while the Atlantic basin may get into the act weeks 2-3 (Saharan dust understood).

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

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).

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

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: