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

Last Updated - 09.21.21 (Routine)


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Global Tropics Hazards and Benefits Outlook Discussion

Last Updated: 09.21.21 Valid: 09.22.21 - 10.05.21
A wave-1 asymmetry continues to be depicted in the upper-level velocity potential anomaly fields across the globe, with enhanced (suppressed) convection across the Indian Ocean, and the Maritime Continent (Western Hemisphere). This pattern has been generally stationary with a slight overall eastward shift when compared to last week’s MJO velocity potential based index. The RMM based MJO index has increased in amplitude compared to last week where the intraseasonal signal is depicted over the Maritime Continent. Upper (lower) level westerly (easterly) wind anomalies have increased across the Pacific, suggestive of an enhanced Walker Circulation, and consistent with a trend toward La Nina conditions. While RMM forecasts from the GEFS and ECMWF ensembles depict a continued eastward propagation of the MJO, with some individual members increasing the amplitude, it is more likely that the enhanced signal is related to the emerging low frequency base state with Kelvin wave activity propagating across the Pacific.

Despite the suppressed convection over the Western Hemisphere, the tropics have remained active across the Atlantic Basin, although recent tropical cyclones (TCs) have been notably weak considering this is the climatological peak of the Atlantic hurricane season. Tropical Storm Odette developed well off the East Coast of the U.S., reaching a peak intensity of 45-mph before becoming extratropical the next day. Tropical Storms Peter and Rose both developed across the central Atlantic on 9/19. Both of these systems are currently active, but are forecast to remain weak. Elsewhere across the global tropics, no new TCs have developed in the previous week.

Continued development across the Atlantic Basin remains forecast with a tropical wave, currently located across the eastern Main Development Region (MDR)(~ 30W). There is a 90% chance of development in the next 5 days according to the National Hurricane Center (NHC), prompting a high confidence formation area in the outlook. Model guidance indicates that this system has the potential to strengthen into a hurricane, possibly breaking the trend of weaker systems that have recently developed over the basin. The remnant low of Odette is also being monitored for possible regeneration into a subtropical storm across the North Atlantic (40% chance in the next 5 days according to NHC). TC development is also possible in the East Pacific (50% chance in the next 5 days according to NHC), but this system is expected to remain weak and far from land.

In the eastern Hemisphere, the enhanced convective envelope over the Indian Ocean favors moderate confidence for tropical cyclone development in the Bay of Bengal toward the end of week-1. Kelvin wave activity over the Pacific also favors increased chances of TC formation tied to invest 99W located near Guam, having a high chance of developing into a TC and tracking north to northeastward in the next week, possibly affecting Japan. There is more uncertainty in week-2 in terms of TC development, although both the GEFS and ECMWF indicate the Main Development Region in the Atlantic remaining active with another system possibly developing towards the end of September.

The highest confidence for above-normal rainfall is posted across portions of the eastern Indian Ocean, southeast Asia, and Maritime Continent during week-1, consistent with the enhanced convective envelope over these areas. Below-normal rainfall is more likely across Central America, the Caribbean, and the Gulf of Mexico. There is more uncertainty in week-2 as the intraseasonal signal continues to become dampened by the evolving low frequency state. Above-normal rainfall remains favored across parts of India and the Maritime Continent, but some drying out is likely across southeast Asia. Uncertainty in the future track of 99W in the West Pacific precludes a confident precipitation forecast, with some GEFS members taking the system close to Japan, and the ECMWF generally keeping the system out to sea. As the Atlantic looks to remain active, enhanced rainfall is forecast across much of the basin. During the week 3-4 period, the CFS and ECMWF indicate the potential for enhanced convection across the basin, which could signal additional TC activity, shifting from the MDR to closer to the Caribbean in accordance with the October TC formation climatology.

The precipitation outlook during the next two weeks is based on a consensus of GEFS, CFS, and ECMWF guidance, anticipated TC tracks, and precipitation composites of past Indian Ocean and Maritime Continent MJO events for Week-1. For hazardous weather concerns during the next two weeks across the U.S., please refer to your local NWS Forecast Office, the Weather Prediction Center's Medium Range Hazards Forecast, and CPC's Week-2 Hazards Outlook. Forecasts over Africa are made in consultation with the International Desk at CPC 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 at 2 PM local Eastern Time 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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