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

Last Updated - 09.27.16 (Routine)


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Global Tropics Hazards and Benefits Outlook Discussion

Last Updated: 09.27.16 Valid: 09.28.16 - 10.11.16
Although the RMM-based MJO index continues to show an enhanced convective signal over the Maritime Continent, the MJO weakened during the past week, with the OLR pattern not reflective of a robust MJO event. The CPC upper-level velocity potential based index depicts a weakening signal, with little eastward propagation. Over the past several days, widespread enhanced rainfall was observed over the eastern Indian Ocean south of the equator, which is not typical during a Phase-5 MJO event during September. Impacts from the negative phase of the Indian Ocean Dipole (IOD), which supports enhanced East Indian Ocean convection due to elevated sea surface temperatures, as well as low-level westerly wind anomalies over much of the Indian Ocean basin, are likely interfering with the intraseasonal signal. Dynamical model RMM-based MJO forecasts are in fairly good agreement predicting a weak signal during the next week, with possible strengthening of the index over the eastern Pacific by Week-2. The potential for a weak signal during Week-1 is supported by a slowly evolving base state favoring suppressed convection over the central Pacific. Therefore, the MJO is not anticipated to play a substantial role in the evolution of the global tropical convective pattern, but may become increasingly influential later in the period. Kelvin wave activity originating from the remnant Maritime Continent enhanced convective envelope may still play a role in potential tropical cyclone formation over the East Pacific during the outlook period.

Two tropical storms developed on 26 September over the eastern and east-central Pacific. Tropical Storm Roslyn formed near 120W and 15N, and is forecast to dissipate over the next week while remaining far from land. Tropical Storm Ulika formed well southeast of Hawaii, and is currently moving to the north-northeast. A turn to the west is anticipated over the next several days, but Tropical Storm Ulika is forecast to weaken to a depression while still far to the east of Hawaii. Typhoon Megi formed northwest of Guam on 23 September and strengthened to Category-4 intensity on the Saffir-Simpson Scale before making landfall over Taiwan as a Category-3 storm. Several fatalities, hundreds of injuries, and extensive property damage were reported in Taiwan due to Typhoon Megi. The storm is forecast to make a second landfall over mainland China early in the period at Category-1 or tropical storm intensity.

Over the next day or two, a low-latitude disturbance east of the Lesser Antilles has a high potential for tropical cyclogenesis. Dynamical model forecasts indicate a potential for impacts across parts of the Caribbean and potentially the mainland US, although there is considerable uncertainty in both the track and intensity forecasts. Later in the Week-1 period, there is a moderate potential for new tropical cyclone development over the East Pacific well south of Mexico, while a weak disturbance over the Bay of Campeche has a low potential to become a tropical cyclone. Over the West Pacific, two disturbances near or east of 150E have a moderate to high potential for tropical cyclogenesis, and may bring enhanced rainfall or winds to Guam. Several dynamical models depict one or both of these systems recurving over the next week or two, which could ultimately affect the mid-latitude pattern over the Western Hemisphere. During Week-2, the overall potential for tropical cyclone formation decreases, although many GFS ensemble members indicate a potential for new a new tropical cyclone forming east of the Philippines.

During Week-1, enhanced convection, possibly partly associated either with the remnant MJO enhanced phase or the IOD, is forecast for parts of the Maritime Continent, while suppressed convection is favored across much of the central Indian Ocean basin. Enhanced rainfall in association with Tyhoon Megi and a mid-latitude front is forecast for parts of China and Japan, while persistent cyclonic flow over South Asia favors enhanced rainfall from eastern India through western Myanmar. Across the Pacific, the low-frequency base state favors suppressed convection just north of the equator, while areas of enhanced convection further north are possible in association with tropical disturbances. Suppressed convection is favored across parts of Central America, while rainfall associated with a tropical disturbance is anticipated over the western Gulf of Mexico and Bay of Campeche and adjacent coastal areas.

During Week-2, a consensus of the CFS and ECMWF dynamical model forecast systems supports enhanced (suppressed) convection across parts of Southeast Asia and the Maritime Continent (South Asia and the southern Bay of Bengal, and the central Pacific). Kelvin wave activity or an emerging MJO signal support a potential for enhanced rainfall over the East Pacific basin, while a mid-latitude frontal system may produce enhanced rainfall across parts of central and eastern Brazil. Enhanced convection is favored by both the CFS and ECMWF across the eastern Gulf of Mexico, although the patterns depicted by each model are quite different.

Forecasts over Africa are generally 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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