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

Last Updated - 12.12.17 (Routine)


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Global Tropics Hazards and Benefits Outlook Discussion

Last Updated: 12.12.17 Valid: 12.13.17 - 12.26.17
The Madden-Julian Oscillation (MJO) presence is mixed depending on whether you evaluate the CPC velocity potential index, which is supportive of an active MJO approaching the Western Hemisphere, or RMM index, which has recently shifted inside the unit circle from Phase 7. Closer inspection of fields that go into the RMM index reveals that the MJO remains present over the Western Pacific, with a particularly robust signal in 850-hPa zonal winds, although the RMM index appears to be having difficulty in isolating the MJO envelope from competing signals of a Kelvin wave moving across Africa and the active phase of an Equatorial Rossby wave in the vicinity of the active MJO envelope. The GEFS appears to overdo the Rossby wave activity in its forecast over the next two weeks, with its RMM index forecasts looping back towards Phase 6 and then shifting back into Phase 7. The ECMWF model appears to be doing a better job of isolating the eastward propagating MJO envelope, increasing the amplitude in Phase 7 during Week-1 and reaching Phase 8 during Week-2. The ECMWF perspective of the MJO is a driving factor in the present outlook, in conjunction with the ongoing La Nina event in the Pacific. Destructive interference between the colocated La Nina event and active MJO envelope reduce confidence in the forecast as the forecast lead time increases.

Over the past week Tropical Storm Four formed in the Bay of Bengal on the 8th of December. This short-lived system drifted northward and brought heavy rain to parts of eastern India and Bangladesh. Prior to developing into a tropical cyclone (TC), this system brought widespread flooding and landslides to Indonesia and Thailand, killing at least 20 people.

Multiple areas exist for possible TC formation during Week-1. The first is in association with a circulation near 9N/132E as of 6 UTC on 12 December, that is forecast to intensify and cross the Phillipines and enter the South China Sea over the next several days. The Joint Typhoon Warning Center gives this system a medium chance of development prior to the forecast period, but confidence is high in the system forming overall. Another system may form between 131-141E and 4-9N late in Week-1, or between this area and the southern Phillipines early in Week-2, with moderate confidence for development. The track of this system is forecast to be similar to the preceding TC, although likely slightly to its south. Elsewhere during Week-1, TC development is possible over the South Pacific between Vanuatu and Samoa. This disturbance is forecast to track eastward and potentially skirt southern portions of Samoa and American Samoa. All of the aforementioned TC development areas are broadly consistent with the MJO tracking from Phase 7 into Phase 8. Lastly, TC formation is possible near northern Madagascar between 45-60E and 10-15S during Week-1. This system is forecast to drift west-southwest before turning southward over the Mozambique Channel. This system is the only one of the aforementioned potential TCs that would not be implicitly linked to enhanced development probabilities from the active MJO traversing the West Pacific.

Multiple areas of anomalous precipitation can be forecast with high confidence during Week-1 due to the active MJO event coupled with the ongoing La Nina. First, the region of anomalously cool sea surface temperatures in the Central Pacific is highlighted for high confidence of suppressed rainfall during both Week-1 and Week-2, generally where anomalies of -1 degree Celsius or greater have been observed. This Week-2 anomalously dry region is reduced spatially relative to Week-1, due in part to increasing potential for destructive interference from the MJO envelope as it potentially enters Phase 8 in Week-2. With expectations for the MJO in Phase 7 during Week-1, this gives high confidence for above-average rainfall from east of New Guinea through the South Pacific and also from the South China Sea into the West Pacific. The suppressed phase of the MJO is favored to be across the eastern Indian Ocean during Week-1, resulting in high confidence for below-average rainfall in this region. Lastly, lagged composites of the MJO in Phase 7 support anomalous dryness for the southwestern U.S. during Week-1, which is also supported by dynamical model guidance that forecasts no widespread precipitation here throughout the next 7 days. High confidence also exists for above-average rains near Hawaii during both weeks due to anomalous troughing from the mid-latitudes in the vicinity of the islands. Remaining areas of anomalous precipitation in Week-1 are due to the anticipated TC developing near Madagascar and otherwise due to agreement among dynamical model guidance.

In Week-2, moderate confidence for above-average rains is possible in a meridionally narrow strip near 10N from the South China Sea through the West Pacific where model guidance suggests a Kelvin wave will pass. This area could be further impacted by the TC formation near the Philippines late in Week-1 or early in Week-2. Elsewhere, moderate confidence for anomalous dryness exists in the Indian Ocean and east of New Guinea as indicated by dynamical model guidance. Lagged mid-latitude impacts for North America tend to be more muted with the MJO over the Western Hemisphere, but could re-emerge beyond Week-2 if the MJO were to make it through the Western Hemisphere and approach the Indian Ocean.

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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