The MJO remained weak during the past week as atmospheric Kelvin waves continue to be the major contributor to anomalous rainfall across the global tropics. Although the amplitude of the RMM index increased recently with the enhanced phase over Africa, the CPC 200-hpa velocity potential index features an incoherent MJO signal. Dynamical model forecasts vary on the evolution of the MJO during the next two weeks. The European ensemble mean depicts a weak to moderate MJO propagating east from Africa to the Indian Ocean, but the GFS model and many of the ensemble members from the Canadian model indicate a continued weak signal with little or no eastward propagation. Based on the model consensus and recent diagnostic tools, the MJO is expected to remain weak during the next two weeks and not play a major role in anomalous rainfall and tropical cyclone activity across the global tropics.
Tropical cyclone development was limited to the Atlantic Basin during mid-June. On June 19, Tropical Storm Bret formed at a low latitude and near the Windward Islands (9.4N/59.8W). This origin of development, so far to the east, is unusual for this time of year. Tropical Storm Bret is forecast to bring heavy rain (2-4 inches, locally more) to Aruba, Bonaire, Curacao, and the northern coast of Venezuela during the next 24 hours before increasing wind shear weakens Bret over the Caribbean Sea. Tropical or subtropical cyclone development is imminent across the Gulf of Mexico as surface pressures slowly fall and deep convection begins to develop around an area of low pressure. Vertical wind shear, associated with an upper-level low near the Texas Gulf Coast, is expected to limit strengthening of the tropical or subtropical cyclone as it tracks north towards the Gulf Coast. During the next week, heavy rainfall (up to 10 inches or more) is forecast for the western and central Gulf Coast, lower Mississippi Valley, and parts of the southeastern U.S.
An atmospheric Kelvin wave is likely to result in above-average rainfall across parts of western Africa and the Ethiopian highlands. Following an increase in rainfall across central India this past week, model guidance indicates that rainfall associated with the Indian Monsoon will be near or below-average through at least Week-1. Above-average rainfall is likely along a stationary front across southern China during Week-1, while below-average rainfall is favored for parts of the Maritime Continent and West Pacific.
During Week-2, the favored areas of anomalous rainfall are based primarily on guidance from the CFS model due to large uncertainty on the MJO evolution and generally small precipitation anomalies from the European model. The most likely area for below-average rainfall exists across parts of the Maritime Continent, while convection is expected to increase across parts of the East Pacific. Forecast confidence in these precipitation shapes is moderate at best due to uncertainty on how different modes of subseasonal tropical variability interact at this time scale.
The GEFS tool indicates that an area east of Philippines may become more favorable for tropical cyclone development by Week-2. Elsewhere, tropical cyclone activity is expected to be near or below climatology.
Forecasts over Africa are made in consultation with CPCs international desk, and can represent local-scale conditions in addition to global-scale variability.
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.