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).

Tropical convective forcing is still enhanced across portions of the Tropical Northwest Pacific Ocean (TNWP; including Super Typhoon Jangmi approaching Taiwan) and the Western Hemisphere. In fact, a respectable surface westerly wind event has been occurring north of Indonesia off the equator. Strong suppression continues across the equatorial Indian Ocean into Indonesia. An important monitoring issue heading into boreal winter will be if westerly wind events accompanying any additional coherently eastward shifting tropical convection across the west Pacific Ocean occur on the equator.

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 Western Hemisphere, not cyclones. Again, this tells us that the WB (2008) GWO (which considers the MJO) is “calling the shots”. Our current Western Hemisphere signal of tropical forcing was initiated by the midlatitude RWDs linked to the positive global mountain torque per above roughly 2 weeks ago.

There is no change in my predictive thoughts from what I typed a week ago. Tropical convective forcing is already festering across the South Indian Ocean. I expect a rapid increase of enhanced rainfall across much of the equatorial Indian Ocean during the next 1-2 weeks. The WH (2004) measure of the MJO is probable to orbit into octants 2-3 over the next few weeks. The WB (2008) GWO is likely to continue its ~10-20 day circuits from phases 4-5 to 8-1, but weakly “spiral” closer to octant 3 of phase space, also during the next few weeks. Hence coupling between the tropics and extratropics could resume by about the middle of October, and the GWO and MJO phase 3 250mb psi snr plots may broadly represent the global circulation.

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 Caribbean, and a central states trough.

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, Mississippi and Ohio Valleys going into this upcoming boreal winter.

The tropical cyclone risk should hopefully decrease across the TNWP after week-1, while staying at least climatology for the Western Hemisphere “until further notice”. In addition to cyclogenesis from the deep tropics, I have concerns for hybrids especially around the Caribbean. After weeks of flooding, etc, suppression (dryer weather) is probable to shift northeast into northern India and Southeast Asia ~weeks 2-3. Per above, intense to severe thunderstorm activity is probable to erupt across the equatorial Indian Ocean during the next 1-2 weeks, then propagate east afterward. The risk of Bay of Bengal and Arabian Sea tropical cyclogenesis should be at least climatology during October.

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

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:

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! I should be able to do a discussion next weekend, ~4-5 October.

Ed Berry

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.

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).

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).

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

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

Ed Berry

Saturday, September 13, 2008

The Great Wall has Risen

“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 Tropical Northwest Pacific Ocean (TNWP) still has the warmest SSTs globally, with totals ~30-31C east of Philippines and anomalies at least plus 1-2C. The equatorial Indian Ocean is also warmer than climatology, as are portions of the Caribbean into the Tropical Atlantic Ocean.

Somewhat characteristic of a mature La-Nina, well defined spatial horseshoes of anomalous SST warmth and coolness emanate from the equatorial west central Pacific Ocean and Dateline regions, respectively, into the extratropics (PDO notions understood). Negative SST anomalies across the latter are at least 2C, having totals cooler than 28C. Thus there is an enhanced east-west SST gradient from the Dateline into the Indian Ocean. Additionally, the equatorial central and east Pacific Ocean thermocline continues to be anomalously shallow allowing subsurface anomalies of less than minus 3C at ~150m deep/155W per TAO buoy data. In fact,this observation is similar to about a year ago.

It appears probable that additional episodes of trade wind surges around the equatorial Dateline generating upwelling oceanic Kelvin waves will continue going into the boreal 2008-09 winter. Hence, while the official ENSO discussion acknowledges that a return to a weak La-Nina is possible, I do not think “ENSO-neutral conditions are expected to continue through the end of 2008” is a scientifically complete statement. As mentioned previously, it is the global tropical SSTs that must be considered when discussing circulation dynamics, not just “Nino 3.4”. Furthermore, the coupled global weather-climate system is already in “a non-lingering La-Nina mode” (more said 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).

Full disk satellite imagery and other tools show tropical convection remains enhanced across the Eastern Hemisphere. The latter is centered ~10-15N/120E, extending from the Bay of Bengal east-southeast to New Guinea and on into the SPCZ. Projection onto a MJO per the WH (2004) methodology is quite strong, roughly 2 sigma in octant 5 of phase space through 12 September. Phase 5 of the OLR composite anomaly snr done on the WH (2004) MJO index reasonably depicts the spatial pattern of tropical convection. The projection reduces to about 1.5 standard deviations in phase 4 retaining the interannual component. However, consisting of 3 subseasonal events since June, there has been at least a 1 standard deviation shift toward the Indian Ocean/Maritime Continent. This is suggestive of a base state returning to “La-Nina”.

Consistent with the above, the Eastern Hemisphere tropical forcing has significantly slowed its eastward propagation, while shifting much more toward the north. While I do expect a weaker MJO signal to propagate into the Western Hemisphere during the next few weeks, our current subseasonal event is likely to be truncated. Tropical forcing is probable to become somewhat enhanced around the Americas ~weeks 1-2, then particularly so from the Atlantic into the Indian Oceans perhaps weeks 2-3.

Relative to WH (2004) phase space, I think the MJO signal will orbit through the “1 sigma circle” and emerge into phases 8-1-2 by roughly late this month. Again, timing and details are noise, especially given recent Western Hemisphere issues, and uncertainty remains non-trivial. However, summing up: 1) centered on 10 September, phase 5 of the MJO streamfunction (psi) composite anomaly snr plot currently depicts the tropical and PNA circulation characteristics; and 2) roughly phase 1 is probable ~days 10-20 for all fields, essentially bypassing phases 6-7. Interestingly, there is some numerical and statistical model support for (2).

Observationally, animations of upper tropospheric daily mean vector wind anomalies do show twin anticyclones ~150E and rapidly decaying cyclones just east of the Dateline. In fact, around 9 September there were ~20-30m/s westerly wind anomalies at 150mb near the Dateline. As these westerlies attempted to propagate eastward, they literally hit a downstream “wall of anomalous easterly wind flow anomalies”. Outflow from Hurricane “Ike” (pointed out by Weickmann) was involved with these easterlies. This is the second observation of this type of behavior during the last few months. I do think there are some complicated feedback issues between the interannual component of the global circulation base state and on-going subseasonal activity. While the WB (2008) GWO captures some of these dynamical processes, there is much work to be done to completely understand them.

In any event, the anomalous equatorial westerly wind flow from 9 September is propagating rapidly into the midlatitudes via dynamical processes explained by the WB (2008) GWO. More specifically, Rossby wave energy dispersions (RWDs) linked to a recent strong positive clustered global mountain torque event (~30 Hadleys) have interacted with these westerlies. A regional-scale response has been the (expected) return of the “western USA (wicked) ridge from Hell” PNA pattern, shown by the GWO phase 5 psi composite.

Cutting to the chase, forced by the mountains and tropical convection, global relative AAM tendency spiked to ~plus 30 Hadleys a few days ago, causing the actual AAM to peak near the R1 data climatology. The response in the WB (2008) GWO phase space was for an orbit to octants 4-5 having ~1.5 sigma projection. Consistent with the equatorially confined empirical WH (2004) MJO signal (due to tropical-extratropical coupling), the WB (2008) GWO is probable to collapse toward octants 8-1-2 during the next 1-3 weeks as AAM tendency becomes negative. Hence it is probable that phases 8-1-2 of the WB (2008) GWO composite anomaly psi snr plots will be representative of the global circulation by ~weeks 2-3. Synoptically, that means the North Pacific Ocean jet should anomalously expand then collapse into some form of a western and central USA trough(s) during the next few weeks.

All of these notions are consistent with my last 2 postings, and are starting to remind me of what I wrote during the 2007-08 boreal cold season. In general, until I “see something different”, it is looking more likely that a “weaker rendition” of our low AAM “La-Nina” base state is coming back for this upcoming (2008-09) cold season. The WB (2008) dynamical global measure of the atmospheric circulation, GWO, may continue its ~10 to 20-day orbits while drifting toward a state shown by the phase 3 GWO psi composite anomaly, representative of a positive Branstator (2002) circumglobal teleconnection. This suggests western and central USA troughs, but with added subtropical westerly wind flow compared to last winter. Weather ramifications should be understood; however, hopefully the southern High Plains will get some decent precipitation this cold season, instead of drought.

Much of the lower 48 states will see a break next week from the recent extremely intense high-impact weather. Per above, a more active regime focusing on the western and central states may return particularly later week-2 and week-3, especially if tropical moisture transport through the Gulf of Mexico improves. GWO phases 8-1-2-of the 2m air temperature composite anomaly snr plots give a nice evolution of that parameter across the USA during the next 1-3 weeks.

While the equatorial Indian Ocean is likely to remain suppressed through at least week-1, much of Southeast Asia and the TNWP should have enhanced rainfall. Included is a risk for more northwest Pacific Ocean tropical cyclones. At some point attention will also need to be paid to the Bay of Bengal.

Next week, the tropical Atlantic Ocean will continue to “sputter” in terms of tropical convection including possible cyclones. Per above, weeks 2-3 should see a return to intense to severe clusters of thunderstorms perhaps focusing on Africa and the equatorial Indian Ocean, while lesser activity hangs around the TNWP and Americas. Relative to climatology, the risk of Atlantic Ocean tropical cyclones may increase weeks 2-3. Further, hybrid systems may become an increasing concern, especially in the region of the Caribbean, as boreal autumn progresses.

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, where WB formally introduce the GWO (WB(2008)), has been accepted for publication in MWR. The authors are in the process of resubmitting after minor revisions. A pdf version (before revision) 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! I will probably not be able to do another complete discussion the weekend of ~27-28 September.

Ed Berry

Saturday, September 06, 2008

Still Tilting Toward an El-Viejo Reprisal (The Dog Rules)

“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). There have been on-going map room issues causing missing data and unrepresentative plots.

The warmest SSTs globally persist across the Tropical Northwest Pacific Ocean (TNWP) with totals exceeding 30C east of the Philippines and anomalies at least plus 1-2C. The on-going trade wind surge at the equatorial Dateline has led to ~minus 2C anomalies having totals less than 28C. As discussed below, these relatively cold SSTs must be a consideration to the characteristics of any eastward propagating MJO signal.

Subsurface negative anomalies continue to shift east along the equatorial East Pacific Ocean thermocline (~4C at 140W/125m per TAO data), responding to an upwelling Kelvin wave generated during July. A similar response may occur with the current trade surge.

Finally, it is my feeling that the JJA ONI of -0.1C based on Nino 3.4 does not scientifically completely represent the interannual component of the global weather-climate situation. The roles of other tropical ocean basins and their impacts on global circulation dynamics must be considered.

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).

Full disk satellite imagery and other tools indicate there has been a slow coherent eastward shift of Eastern Hemisphere tropical convection during ~the last 25 days. A convectively coupled Kelvin wave preceded this rainfall, and appears to be propagating into the Western Hemisphere. The region of enhanced convection is centered on about 5N/120E, extending from the eastern Arabian Sea east-southeast into the west central Pacific Ocean. A "back of the envelope calculation" gives a phase speed of ~3.5-4m/s (~3 deg long/day).

The WH (2004) methodology gives roughly a 1 sigma projection in octant 4 of phase space, and nearly a 1.5 standard deviation shift in octant 3 leaving the base state in. Phase 4 of the composite streamfunction (psi) anomaly plots centered on 3 September nicely represent current tropical and even PNA circulation anomalies. I think the latter is true given a growing MJO signal. However, I also think the interannual component will remain significant.

Global relative AAM is still well below the R1 data climatology, more than 1 sigma (~1 Atmospheric Momentum Unit (AMU)), removing the stratospheric westerly phase of the QBO, through 3 September. Using this same measure (no QBO signal), relative AAM is still up about 2 AMUs compared to a year ago, meaning more subtropical westerly wind flow. However, Rossby wave trains interacting with the tropical convective forcing and midlatitude mountains (explained by the WB (2008) GWO) have led to a strong negative AAM tendency of roughly 15 Hadleys. Much of this negative AAM tendency is coming from the Southern Hemisphere. Hence the WB (2008) GWO continues to “hover” around octants 1-3 of phase space.

Constructively interfering with the MJO signal, phase 3 of the GWO composite psi anomaly plot is representative of the on-going “Branstator (2002)-like” positive phase of a circumglobal teleconnection. The subtropical sink-midlatitude source AAM transport signal, strong in the Southern Hemisphere and weak for the Northern Hemisphere, support this notion. Synoptically this means our global circulation base state favors stronger than normal subtropical and midlatitude ridges.

So, where does the global circulation go from here? First, I think there is some coupling between the GWO and the MJO. Secondly, and arguably not emphasized enough and stating redundantly, I think there is an eastward propagating Eastern Hemisphere MJO signal.

Most models suggest propagation into roughly octants 5-6 of WH (2004) phase space by late week 2 or 3. Given the cold Dateline SSTs and other reasons I have, I agree with the eastward shift, but possibly truncated. The enhanced tropical forcing is probable to propagate east-northeast, focusing on the warm TNWP by ~week 3. A weaker MJO signal should then continue into the Western Hemisphere afterward. Emphasizing from past discussions, should this and other subsequent subseasonal events lead to eastward propagation of tropical convective forcing along the equatorial West Pacific Ocean, a slow (interannual time scale) evolution to a warm event is possible.

The WB (2008) GWO is likely to continue its 10-20 day periodicity orbiting from octants 8-1 to 4-5 in phase space, leaning toward low AAM, while “riding along” with the MJO signal. Phases 4-5 of the MJO psi (and temperature) composite anomaly plots appear reasonable for weeks 1-2. Phases 6-8 may be representative for ~weeks 3-4. Regardless of the white noise details and timing, 1) I am concerned another prolonged period of Western Hemisphere-Indian Ocean active convection is possible after week-two (MJO phases 8-1-2), and 2) at some point there is likely to be an anomalous extended North Pacific Ocean jet collapsing into a western USA trough, like that shown by phases 8-1 of the WB (2008) GWO. Keeping in mind issues of boreal autumn, the latter may be most probable the last 10 days of this month into early October. My confidence is still low in the outlooks that follow.

Per above, currently much of the USA is being dominated by an anomalous trough centered ~100W. Most numerical models significantly underestimated this feature a couple of weeks ago (discussed in my last 2 postings). I agree the trough will persist roughly week-1, in the presence of synoptic events. Ridging is probable to return to the western states while the trough moves into the eastern USA week-2 (phases 4-5 of the GWO composites). Weeks 3-4 were discussed above. The probable temperature outcomes can be seen from the composite anomaly plots.

Again, possible impacts onto the USA from additional tropical cyclones including “Ike” remain a concern, and please see the latest official statements from the Tropical Prediction Center. I think the North Atlantic Ocean tropical cyclone hazard may decrease to below climatology by ~week 2, and then perhaps increase afterward.

In general, heavy precipitation is likely for much of the country east of the Rockies next week. Climatology going into October suggests generally dry weather for much of the country, and that should be the case for at least approximately week-2. A more active situation may return for the western and eventually central states weeks 3-4. My thoughts for this coming cold season remain unchanged (see 30 August posting).

As already discussed, intense to severe tropical thunderstorm activity is likely to propagate east and northeast initially impacting Southeast Asia and Indonesia, then focusing on the Philippines by week-3. Portions of the equatorial Indian Ocean may see a break from the recent rainfall by week-2. While a "wild card" until further notice, the tropical cyclone hazard is probable to increase above climatology for the TNWP weeks 2-3. For various reasons, the East Pacific Ocean ITCZ and Americas will be “sporadic” in terms of enhanced convection, possibly becoming active by weeks 3-4. Equatorial Africa may be somewhat suppressed weeks 1-2.

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