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

Last Updated - 08.17.18 (Update)


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Global Tropical Hazards/Benefits Assessment

Global Tropics Hazards and Benefits Outlook Discussion

Updated discussion
Last Updated: 08.17.18 Valid: 08.18.18 - 08.28.18
The MJO as monitored by both the RMM and CPC velocity potential index weakened over the past few days. This was expected as various convective signals are competing over the global tropics. The latest ensemble guidance suggests that a coherent enhanced phase may emerge over the Maritime Continent and propagate over the West Pacific by the end of Week-2. This is due to the fast eastward propagation of a Kelvin wave into the Eastern Hemisphere as well as the developing El Nino base state.

Tropical Storm Rumbia and Typhoon Soulik formed over the West Pacific as forecast during the past few days. Tropical Storm Rumbia made landfall late August 16 near Shanghai, while Typhoon Soulik is forecast to track northwestward while intensifying to the equivalent of a category 3 on the Saffir-Simpson scale. A landfall over southern Japan on August 21 is currently forecast by the Joint Typhoon Warning Center. Over the East Pacific Hurricane Lane formed as a depression at 00Z August 15. It is forecast to take a track similar to Hurricane Hector, tracking nearly due west near 15N, passing south of Hawaii by the middle of next week. Subtropical Storm Ernesto formed near 38N over the North Atlantic on August 15, and is rapidly moving northeastward, forecast to become post-tropical by later today.

Tropical cyclone (TC) formation is highly likely over the West Pacific in the next day or two, about 10 degrees east of where Typhoon Soulik formed. Over the East Pacific, there is a low risk of TC formation east of Hurricane Lane. Over the Atlantic basin TC formation remains unlikely over the next 10 days or so. During the modified Week-2 period, TC formation is still possible over the West Pacific based on the various ensemble guidance. Over the East Pacific, some lull appears likely in the wake of the recent burst in activity and as the enhanced convective signal shifts toward the Maritime Continent.

Areas favoring above- or below-average rainfall were adjusted based on the latest guidance from the ECMWF, GEFS, and CFS ensemble systems, as well as forecast TC tracks.

The previous discussion issued August 14 follows below:
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The large-scale global tropical pattern remains fairly stationary this week, reflecting conditions similar to an intraseasonal event centered over the Pacific. Widespread convection continues across East and Southeast Asia and across the Pacific, and any propagation has been more northward than eastward. The RMM-based MJO index has been somewhat erratic, but has remained outside of the unit circle over the past two weeks in Phases 6 or 7. The CPC velocity potential based MJO index also indicates an enhanced (suppressed) convective phase over the Pacific (Africa and Indian Ocean), which is similar to the position of the MJO during mid-July. Analyses of low-level zonal wind anomalies reflect a persistent regime of weakened trade winds across the equatorial Pacific, part of which is due to tropical cyclone activity, but may also indicate a shifting atmospheric base state towards El Nino conditions. Additionally, a robust, convectively coupled Kelvin wave is currently crossing the eastern Pacific. Dynamical model MJO index forecasts generally depict a weakening MJO signal during Week-1 as convection shifts toward parts of the Indian Ocean for a brief time (due in part to an equatorial Rossby wave) and the aforementioned Kelvin wave tracks back in to the eastern Hemisphere. By Week-2, most dynamical models agree that an eastward-moving enhanced subseasonal signal is likely near the Maritime Continent.

The West Pacific basin has been extremely active during the past week. Hurricane Hector, now a weakening tropical storm, crossed the Date Line and is now in the West Pacific. All other tropical cyclones in the East Pacific have dissipated over the past week. Tropical Storms Leepi and Bebinca developed over the West Pacific and South China Sea, respectively. During Week-1 tropical cyclogenesis is most likely over the East Pacific, where NHC indicates a 90% chance of development over the next five days. Over the West Pacific, two areas are currently being monitored for development: one in the vicinity of Guam, the other northeast of Taiwan. Over the North Atlantic, NHC indicates a 40% chance of subtropical storm development near 35-40N and 40-50W. During Week-2, the only area with notably enhanced odds of tropical cyclogenesis is near and east of Guam, where the low-frequency state remains very favorable.

The forecasts for above- and below-average rainfall were based primarily on a consensus between the CFS, GEFS, and ECMWF, as well as official guidance from the NHC and JTWC where precipitation is due to existing tropical cyclones. During Week-1, wet weather is favored to continue across parts of Southeast Asia, the South China Sea, the northern Philippines, and over much of Japan, while near- to below-average rainfall is anticipated across parts of the equatorial Maritime Continent. Areas of enhanced rainfall due to tropical cyclones and an enhanced ITCZ are forecast across parts of the central and eastern Pacific. Below-average rainfall is favored along Mexico's southern coast, Central America, and the far eastern Pacific due to subsidence in the wake of forecast tropical cyclogenesis and the atmospheric Kelvin wave.

During Week-2, uncertainty increases as expected, with some model divergence and an unclear picture of subseasonal variability. Above-average rainfall is more likely over parts of the eastern Indian Ocean extending northeastward toward Taiwan and the Philippines, and enhanced convection also becomes more prominent over the eastern Maritime Continent and parts of the Pacific. This is due to both the forecast evolution of the subseasonal variability (uncertain as it is) as well as the developing low-frequency state. Models are in fairly good agreement on continued below(above)-average rainfall over parts of the East Pacific, Central America, and northern South America (western Brazil).

Forecasts over Africa are made in consultation with the CPC 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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