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

Last Updated - 05.23.17 (Routine)


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Global Tropics Hazards and Benefits Outlook Discussion

Last Updated: 05.23.17 Valid: 05.24.17 - 06.06.17
During the past week, both the CPC velocity potential anomaly based index and the RMM index indicate eastward propagation of a weak subseasonal signal over the Indian Ocean. Low-level (850-hPa) westerly wind anomalies recently developed just north of the equator in the North Indian Ocean, while easterly wind anomalies persisted over the western Pacific, at about the same low latitude. This implies convergence of mass across the area of the Maritime Continent, leading to rising motion. Upper-level (200-hPa) zonal wind anomalies are of the opposite sign to those at low levels from the eastern Indian Ocean to near the Date Line, implying the divergence of mass at the upper levels of the troposphere. The outgoing longwave radiation (OLR) anomaly field depicts the recent development of enhanced tropical convection across the tropical Indian Ocean and the Maritime Continent, and suppressed convection across much of the tropical Pacific. The OLR anomaly field also depicts a slight eastward displacement (from climatology) of the South Pacific Convergence Zone (SPCZ).

Most dynamical models predict that other modes of tropical variability (in particular, Equatorial Rossby Waves or ERWs) will obscure the MJO signal as it traverses the Indian Ocean basin and the Maritime Continent over the next two weeks. Some models redevelop an eastward-moving convective signal over the Indian Ocean during Week-2, with a few (particularly the European model) taking the intraseasonal signal across the Maritime Continent. The Indian Ocean Dipole (IOD), which had been in a persistent negative phase, is now in its neutral phase, according to the Australian Bureau of Meteorology (BoM). The BoM predicts the IOD will become positive during the next few months, which would be associated with abnormally warm sea surface temperatures (SSTs) and enhanced convection over the western portion of the Indian Ocean basin.

Only one tropical cyclone (TC) was in progress during the past ten days across the global tropics; Ella, a minimal category 1 Cyclone over the South Pacific (09-14 May). Ella tracked northwestward between Fiji and American Samoa, bringing heavy rain and strong winds to the nearby islands of Wallis and Futana. During the next two weeks, the best chance for a TC to develop is over the Bay of Bengal, according to the ECMWF and GFS models, Taiwan's TC tracker tool, and subseasonal signals. The latest ECMWF model run predicts the formation of a low pressure center around 0z on 27 May off the coast of Burma/Myanmar. Over the ensuing few days, the budding disturbance intensifies and tracks northward, reaching the Bangladesh/Myanmar coast on 31 May. The latest GFS solution forecasts the development of a weak Low over the central Bay of Bengal around 12z on 29 May, which then tracks northward towards the Bangladesh coast, yet remains weak in intensity. The GFS has shown fairly poor day-to-day continuity regarding the evolution of this potential TC. The TC tracker tool from the Central Weather Bureau in Taiwan also favors potential TC activity in the Bay of Bengal region.

During Week-1, areas of above-average rainfall are predicted (with moderate confidence) across parts of the central and eastern Indian Ocean, Southeast Asia, and parts of the Maritime Continent due to the expectation of a subseasonal signal progressing into this region. The MJO signal is forecast to be partially masked/obscured by other modes of tropical variability, such as ERWs and Kelvin Waves. Enhanced rainfall is possible across the Andaman Sea and eastern Bay of Bengal, associated with the potential development of a TC. Other areas of above-average rainfall are predicted off the U.S. East Coast and Florida (high confidence), and in southern Brazil/Uruguay (moderate confidence); both are attributed to influences expected from mid-latitude baroclinic systems.

During Week-2, three areas of above-average rainfall are forecast (with moderate confidence) across the North Indian Ocean/Maritime Continent region, due to suspected MJO activity, along with some interference from other modes of tropical variability (ERWs and Kelvin Waves). Another area of predicted above-average rainfall is over the south-central contiguous U.S. (with moderate confidence) due to mid-latitude frontal activity. Below-average rainfall is anticipated over the far eastern Pacific, just west of Central America, with moderate confidence. This area, along with all the other predicted regions of anomalous precipitation for both Week-1 and Week-2, are primarily based on areas of agreement between ECMWF and GFS model forecasts for rainfall.

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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