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

Last Updated - 04.18.17 (Routine)


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Global Tropics Hazards and Benefits Outlook Discussion

Last Updated: 04.18.17 Valid: 04.19.17 - 05.02.17
Over the prior week the RMM index suggested that a Madden-Julian Oscillation (MJO) event emerged in the Western Hemisphere, but exhibited little to no eastward propagation. The CPC velocity potential-based MJO index is less robust, particularly with the 15-day running mean. The discrepancy appears due to the signal in the RMM index being tied to a Kelvin wave presently in the East Pacific. Dynamical model RMM forecasts are mixed, but those that maintain amplitude of an intraseasonal event in the Western Hemisphere generally lack eastward propagation and instead keep a signal in Phases 7 or 8 throughout the next two weeks. This gives further support to the lack of an active MJO event, and thus any MJO influence on the tropics or subtropics is not anticipated during the forecast period.

A pair of short-lived tropical cyclones developed over the past week: Tropical Depression Two in the West Pacific and Tropical Storm Maarutha in the Bay of Bengal. Tropical Depression 2 formed on 14 April near 11N/130E and brought heavy rains to the Central Philippines before dissipating the next day. Maarutha developed on 15 April and tracked northeastward into Myanmar, making landfall with 35 kt winds. Heavy rains from Maarutha helped yield flash flooding and mudslide concerns across Myanmar.

No circulations are presently apparent in satellite imagery that would suggest near-term tropical cyclone development. The National Hurricane Center is monitoring an extratropical system near 32N/45W for possible development into a subtropical storm, giving this a 30% chance of occurring in the next 5 days. No impacts from this system on the U.S. are anticipated. Dynamical model guidance does track a pair of twin disturbances on either side of the equator late in Week-1, that bear monitoring for tropical cyclogenesis. This appears tied to the potential emergence of a Kelvin wave near 120E by the middle of Week-1, with twin circulations possible off the equator in its wake. The first targeted area stretches from the Philippines eastward to near 145 E between 5-15N with support from both the GEFS and ECMWF ensemble guidance. The second area is the Arafura Sea between approximately Darwin and the eastern extent of the Gulf of Carpentaria, where again each ensemble suite suggests development of a westward tracking system near the end of Week-1. Both areas are given moderate confidence of development, with slightly higher odds presently favored for the disturbance in the West Pacific.

Given the limited sources of observed intraseasonal variability in the tropics aside from the present active Kelvin wave, dynamical model guidance is relied upon heavily in the existing outlook. This limits confidence in forecast features to moderate across the board, due to limited ties between physical phenomena. The best signal appears to be that of an emerging Kelvin wave in the vicinity of the Maritime Continent by the middle of Week-1 that is indicated by dynamical model guidance, with these features typically underestimated by the models. Twin Rossby waves are possible in the wake of this feature, giving rise to the aforementioned tropical cyclogenesis threats, and above-average rainfall for the eastern Maritime Continent and West Pacific. Below-average rainfall is possible in the northern Central Pacific in both weeks centered on 10N, where conditions have been persistently dry the past several weeks. Enhanced convection has been fairly consistent across portions of the South Pacific over the last month, with above-average rains possible for parts of the region in Week-1 and Week-2. Anomalously dry conditions are also anticipated off the west coast of the U.S. during Week-2, along and downstream of an anticipated 500-hPa ridge axis in this vicinity. A drying trend is also anticipated across much of Southeast Asia throughout the forecast period, with below-average rain forecast here during Week-2.

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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