The MJO remained active during the past two weeks, propagating rapidly across the Pacific before returning to the Western Hemisphere. During the past several days, the RMM index stalled over the Western Hemisphere. This slowdown is likely due to constructive interference between the MJO and the strong positive phase of the Indian Ocean Dipole (IOD). Dynamical model forecasts of the RMM index are mixed, although most depict weakening with no additional propagation to the eastern Indian Ocean or Maritime Continent during the next two weeks. In addition to the IOD which favors convection over Africa and the western Indian Ocean, robust Rossby wave activity and above-normal SSTs across the central Pacific may help generate additional convection that is out of phase with the current MJO event. This may be why some GFS and ECMWF ensemble members favor a quick return of the index to the Pacific. Based on these forecasts, the MJO is favored to play a diminishing role in the evolution of the tropical convective pattern over the outlook period. The IOD will likely become the dominant mode of tropical variability, and widespread convection over the western Indian Ocean may teleconnect to the midlatitudes and help change the downstream pattern over North America with more troughing across the West.
Tropical Depression 21-E formed over the East Pacific and dissipated over open waters. The remnants of earlier Tropical Storm Raymond are expected to generate a very late season Gulf moisture surge into the U.S. Southwest. A late-season tropical cyclone also formed over the Atlantic well northeast of the Lesser Antilles: Tropical Storm Sebastian, which is forecast to move generally northward for a couple of days before merging with a frontal system. Over the West Pacific, Tropical Depression 28-W recently formed, and forecasts from the Joint Typhoon Warning Center bring this system towards or just north of Luzon in the Philippines. This path is very close to the current location of Tropical Storm Kalmaegi. During the next two weeks, robust Rossby wave activity over the central Pacific may help generate new tropical cyclones both north and south of the equator. Dynamical models favor the potential for tropical cyclogenesis between Guam and the Philippines, close or east of the current location of TD 28-W. Enhanced convection just west of the Date Line may provide another source for tropical cyclone development as well, so both of these regions are covered in a broad moderate confidence forecast area. Additionally, dynamical models favor tropical cyclone development over the Southwest Pacific west of American Samoa. Should a tropical cyclone form in this area, it may impact Fiji. These same areas are highlighted for potential tropical cyclone formation in Week-2 as well due to the uncertain timing for formation. No new tropical cyclone activity is anticipated for the East Pacific or Atlantic basins.
Precipitation forecasts are reflective of the Western Hemisphere MJO event, a strong atmospheric response to the IOD, and an active Pacific due to Rossby wave activity and above-normal SSTs. Widespread above-normal rainfall is favored across eastern Africa and the western Indian Ocean, and anomalies depicted by the dynamical models are quite high. There is a potential for high impact flooding across affected regions of eastern Africa. Subsidence and below-normal SSTs favor widespread suppressed convection across the Maritime Continent, while an enhanced and northward-displaced ITCZ is favored across the western and central Pacific. Precipitation forecasts across the Western Hemisphere are based on a consensus of the ECMWF and CFS forecasts, and favor suppressed (enhanced) rainfall for Central America (northern South America). Precipitation forecasts for Week-2 are broadly similar to Week-1 due to the low-frequency IOD being the dominant mode, although the ECMWF favors a transition to wetter conditions across Central America.
Product Release Information
The full Global Tropics Hazards and Benefits Outlook (GTH) is released once per week every Tuesday at 1730 UTC (1830 UTC when on standard time) including U.S. federal holidays. At the time of product release, there is a live briefing (available via webinar) open to all interested parties in which the latest conditions in the Tropics and the just released outlook and associated impacts are discussed. There is an opportunity to ask questions after the briefing and the briefings are available at the Live Briefing Archive and soon will be recorded.
CPC also issues an operational update of this product every Friday by 1730 UTC to further support the NWS regions. The update only spans the release period from June 1 through November 30 and a region from 120E to the Prime Meridian in longitude and from the equator to 40N in latitude. The update does not extend the time horizon of the product, but rather applies for the remaining 4 days of the previous Week-1 time period and Days 5-11 from the previous Week-2 period. This page will depict both the original and updated outlook maps as well short text outlining the forecast rationale for any changes.
The Global Tropics Hazards and Benefits Outlook is a forecast for areas with elevated odds for above- or below-median rainfall, above- or below-normal temperatures and regions where tropical cyclogenesis is favored for the upcoming Week-1 and Week-2 time periods. The rainfall outlook is for precipitation integrated over a week and targets broad-scale patterns, not local conditions as they will be highly variable. Above(below) median rainfall forecast areas are depicted in green and yellow respectively. Above(below) normal temperature forecast areas are depicted in orange and below respectively. Favored areas for tropical development are shown in red. Two measures of confidence are indicated, high (solid) and moderate (hatched) and are currently subjective in nature and not based on an objective system. Work towards a probabilistic format of the product and so an objective measure of confidence is ongoing. The weekly verification period ranges from 00 UTC Wednesday to 00 UTC the following Wednesday.
Along with the product graphic, a written text outlook discussion is also included at release time. The narrative provides a review of the past week across the global Tropics, a description of the current climate-weather situation, the factors and reasoning behind the depicted outlook and notes on any other issues the user should be aware of. The discussion discusses the impacts in the Tropics as well as potential impacts in the Extratropics when relevant.
Product Physical Basis
The product synthesizes information and expert analysis related to climate variability across multiple time scales and from various sources, including operational climate monitoring products. The physical basis for the outlooks include
El Nino-Southern Oscillation (ENSO) , the
Madden-Julian Oscillation (MJO), strength and variations of the monsoon systems, other coherent subseasonal tropical variability such as atmospheric Kelvin waves (KW), Equatorial Rossby waves (ERW), African easterly waves, as well as interactions with the extratropical circulation (i.e. high latitude blocking, low-latitude frontal activity, etc.).
Product Forecast Tools
The outlook maps are currently created subjectively based on a number of forecast tools, many of which are objective. The final depiction is an assessment of these forecast tools based on a number of factors to create the final product. Work is ongoing to create an objective consolidation of some of the available forecast tools to serve as a first guess for the forecaster. Forecast tools include MJO composites, empirical and dynamical based MJO, ERW and KW forecasts, and raw dynamical model guidance from a number of modeling systems. Tropical cyclone areas are based on MJO composites and statistical and dynamical tropical cyclone forecasts as well as raw model forecast guidance.
The product supports the NOAA mission in three primary ways:
- Assess and forecast important changes in the distribution of tropical convection (i.e., potential circulation changes across the Pacific and North America sectors) and communicate this information to NWS forecasters
- Provide advance notice of potential hazards related to climate, weather and hydrological events across the global tropics (including tropical cyclone risks for several NWS regions)
- Support various sectors of the U.S. economy (finance, energy, agriculture, water resource management) that have foreign interests.
The product is created through collaboration with other NOAA centers, [the National Hurricane Center (NHC) and the Central Pacific Hurricane Center (CPHC)], the Department of Defense [The Joint Typhoon Warning Center (JTWC) and the Naval Postgraduate School (NPS)], the Australian Bureau of Meteorology, Taiwan Central Weather Bureau, the State University of New York at Albany (SUNY) and the Center for Climate and Satellites (CICS), among other collaborators.
Product Users and Applications
Known users include U.S. government agencies such as NOAA [National Weather Service (NWS), River Forecast Centers (RFCs), the National Marine Fisheries Service (NMFS), the Department of the Interior (U.S. Forest Service), aid organizations (U.S. and international Red Cross, USAID), domestic and global private sector interests (financial, energy, water resource management and agricultural sectors), international weather services and various media meteorologists.
Some special applications of the product in the past include extended range predictions to support Haiti earthquake and Deepwater Horizon oil spill relief efforts as well as support for the Dynamics of the MJO (DYNAMO) scientific field campaign held from October 2011 through March 2012.