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HOME > Climate & Weather Linkage > Global Tropics Benefits/Hazards

Last Updated - 02.12.19 (Routine)


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Global Tropics Hazards and Benefits Outlook Discussion

Last Updated: 02.12.19 Valid: 02.13.19 - 02.26.19
The MJO remains active in early to mid-February, with its enhanced convective phase centered over the Pacific Ocean. According to the RMM index, the eastward propagation stalled in Phase 7, due to the interaction between the MJO and a strong equatorial Rossby wave (ERW). A broad envelope of enhanced convection developed recently near the Date Line as a result of the constructive interference among the MJO, ERW, and ENSO. OLR anomalies (between Jan 31-Feb 9) indicate broad-scale enhanced (suppressed) convection over northeast Australia along with the western and central equatorial Pacific (Indian Ocean). Enhanced convection also extends from the subtropical East Pacific near Hawaii northeastward to southern California and the Baja Peninsula, which defines the mean location of several atmospheric rivers that resulted in very heavy snowfall accumulations across portions of the Sierra-Nevada mountain range.

Dynamical model forecasts are in decent agreement that, after briefly interfering with an ERW in Phases 7/8, eastward propagation of the subseasonal signal resumes with enhanced convection progressing east over the Western Hemisphere (Phases 8/1) during the next two weeks. The GEFS and CFS predict very high signal amplitudes during Week-2 in Phase 8; perhaps too high. The ECMWF and Canadian RMM index forecasts have a few ensemble members that reach the Indian Ocean late in Week-2, with fairly moderate signal amplitudes. CFS forecasts of both OLR and 200-hPa Velocity Potential anomalies predict the main bulk of the convective envelope near the Date Line will remain in place during the next two weeks, with smaller-scale bursts of eastward propagating energy across the Western Hemisphere. These smaller-scale features are expected to consist of a broader range of subseasonal modes that are consistent with MJO phase speeds or faster.

The South Indian and South Pacific Ocean basins have seen the development of several tropical cyclones (TCs) during the past 7-10 days. TCs Funani (now defunct) and Gelena (ongoing) formed over the Southwest Indian Ocean near Madagascar, with both attaining peak sustained wind speeds of about 200 km/hr. In the Southwest Pacific, storms included 06F, Neil, and Oma/15P (ongoing). As of this writing, each system had peak sustained wind speeds of 65 km/hr. Areas affected include the Samoan Islands, Fiji, Tonga, and Vanuatu. TC Oma is forecast by the Joint Typhoon Warning Center (JTWC) to move near or across the islands of Vanuatu during the next few days, and possibly near the island of New Caledonia two days later. The influence of the active phase of the MJO and an ERW near the Date Line during the next 1-2 weeks leads to high and moderate risks of TC development over the western and central South Pacific in Week-1, respectively, and the western North Pacific (moderate confidence) in Week-2. ERWs sometimes lead to the formation of twin cyclones that straddle the equator.

The rainfall forecasts for Week-1 and Week-2 are based on areas of agreement between ECMWF and CFS precipitation guidance, and anticipated influence from TCs, ENSO, the MJO, an ERW, atmospheric rivers, and the South Pacific Convergence Zone (SPCZ). During Week-1, above-average rainfall is predicted over the west-central Pacific (10N-25S/150E-160W), associated with the interference between the MJO, ENSO, an ERW, and a TC. Above-average rainfall is also forecast east of Hawaii, with much of this precipitation streaming northeast to California. As one or more of these subtropical moisture plumes or "atmospheric rivers" reaches the mountainous terrain of California, it is likely to result in very heavy snowfall accumulations for the Sierra-Nevadas; some areas may receive 3-5 feet of additional snowfall. The central South Pacific is also expected to see above-average rainfall, associated with the SPCZ and potential TC development. A widespread area of below-average rainfall is anticipated over the Maritime Continent region and adjacent portions of northern Australia, associated with the suppressed convective phase of the MJO and upper-level convergence, and the low-frequency footprint (dry signal) of ENSO. A much smaller-scale region of below-average rainfall is expected near Madagascar, based on ECMWF and CFS precipitation guidance. For Week-2, above-average rainfall is forecast for portions of the west-central Pacific, related to various contributions from ENSO (wet signal), the MJO, potential TC development, and possible ERW interference. As with Week-1 (and for the same reasons noted earlier), a broad area of below-average rainfall is forecast over the Maritime Continent region and far northern Australia. Above-normal temperatures (defined as the upper one-third of the historical temperature distribution) are indicated over much of Western Australia, and portions of the Northern Territory.

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.

Product Description

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.

Product Purpose

The product supports the NOAA mission in three primary ways:

  1. 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
  2. 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)
  3. Support various sectors of the U.S. economy (finance, energy, agriculture, water resource management) that have foreign interests.

Product Partners

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.

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