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Last Updated - 08.07.20 (Update)


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Global Tropical Hazards/Benefits Assessment

Global Tropics Hazards and Benefits Outlook Discussion

Updated discussion
Last Updated: 08.07.20 Valid: 08.08.20 - 08.18.20
The amplitude of the MJO on both the CPC velocity potential and RMM-based MJO indices increased over the past several days, with a substantial dipole of enhanced (suppressed) convection evident over the Maritime Continent (Western Hemisphere), and a robust northwestward extension of the enhanced convection into the South and Southeast Asia monsoon regions. Little eastward propagation of the signal was noted over the past few days, but dynamical models are beginning to come closer into agreement suggesting that robust Kelvin wave (or fast MJO) activity will shift the region of enhanced convection back to the Western Hemisphere by the end of Week-2.



As indicated in the initial outlook, tropical cyclogenesis is likely just southwest of Mexico within the next several days, and the latest NHC tropical weather outlook has a 90 percent chance of formation within the next five days. Given the potential for Kelvin wave activity during the outlook period, additional tropical cyclogenesis is likely for the Week-2 period as well. In fact, the operational GFS depicts three distinct tropical cyclones forming southwest of Mexico during the Week-2 period. Across the Atlantic, significant tropical cyclone activity is not anticipated, but the NHC is currently monitoring a weak tropical wave crossing the MDR. While formation chances are low over the next five days, there is a moderate potential for a brief formation of a tropical cyclone during the Week-2 period before conditions become increasingly unfavorable. Elsewhere, the Joint Typhoon Warning Center is monitoring a disturbance just east of the Philippines for possible development. Dynamical model tracks bring this potential tropical cyclone northward towards southern Japan over the next several days.



The original discussion released on 4 August 2020 follows.

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The Madden-Julian Oscillation (MJO) continued to project well on both the CPC velocity potential based index and the RMM index during the past week. The zonal wind field at both the upper and lower levels of the atmosphere correspond well to a Maritime Continent MJO event, helped in part by midlatitude wavebreaking from the Southern Hemisphere onto the Equator north of Australia. Analyses of recent OLR anomalies centered north of the Equator show interactions between a low-frequency signal favoring enhanced convection over the Indian Ocean, a robust Rossby wave now crossing the Maritime Continent, and Kelvin wave activity moving ahead of the broader envelope to the Pacific. Dynamical model MJO index forecasts diverge considerably, with the GEFS depicting continued fast eastward propagation of the signal across the Pacific, possibly tracking robust Kelvin wave activity, while the ECMWF shows no Pacific signal, but brings the index rapidly back to the Western Hemisphere by Week-2. Despite the uncertainty regarding the future evolution of the signal, the overall MJO-forced pattern is likely to play a role in the global tropical convective field over the next week or two. In particular, the suppressed phase of the MJO may help bring a period of relative quiet to the Atlantic MDR tropical cyclone basin during the outlook period. Beyond Week-2, however, conditions may become more favorable for renewed Atlantic tropical cyclone activity.

On 30 July, Hurricane Isaias developed over the eastern Caribbean, bringing widespread rainfall to Puerto Rico, Hispaniola, and the Bahamas before turning northward just east of Florida. The hurricane weakened to tropical storm intensity after encountering increasing vertical shear, but regained hurricane intensity just before landfall near the South Carolina and North Carolina border. The storm is currently moving rapidly northeastward, bringing impacts to much of the U.S. East Coast. Tropical Storm Sinlaku formed over the South China Sea on 1 August, making landfall over Vietnam and bringing widespread heavy rainfall across the region. On 2 August, Typhoon Hagupit developed east of China, strengthening to Category-1 intensity on the Saffir-Simpson scale before making landfall well south of Shanghai. The remnants of Hagupit are forecast to bring widespread rainfall to parts of northern China, the Korean Peninsula, and western Japan over the next several days. The two West Pacific tropical cyclone formations are strongly tied to the aforementioned Rossby wave now crossing the Maritime Continent.

During Week-1, the NHC is monitoring a disturbance north of Puerto Rico for potential development. Confidence in formation has decreased somewhat as dry air intrusion began limiting convection, but a moderate confidence for formation has been maintained on this outlook due to weak steering currents that will allow the disturbance to stall for most of the week south of Bermuda. Over the East Pacific, dynamical models favor a potential formation southwest of Mexico late in the period, with the threat beginning over the weekend and extending into Week-2. Kelvin wave activity crossing the Pacific may help contribute to this potential formation. Elsewhere, tropical cyclogenesis is not anticipated, but conditions may become increasingly favorable for renewed activity across the Western Hemisphere basins beyond the Week-2 period.

Forecasts for above- and below-average precipitation were based on dynamical model consensus. Consistent with a Maritime Continent MJO event, enhanced monsoon rainfall is favored across parts of South and Southeast Asia during the outlook period, extending southeastward to the equatorial Maritime Continent. In contrast, the low frequency base state favors continued suppressed convection across parts of the West Pacific basin, including the Mariana Islands and Guam, where drought conditions have worsened. Enhanced rainfall associated with frontal interactions with the remnants of Typhoon Hagupit may generate additional floodwaters across parts of the northern Yangtze River basin, though drier conditions are favored for the lower portions of the basin. Storm systems are favored to bring precipitation to Australia's core winter wheat growing regions, while Kelvin wave activity may enhance convection across the East Pacific and Central America. A continued lackluster monsoon is forecast to continue across northwestern Mexico and the U.S. Southwest.

During Week-2, enhanced rainfall is favored to persist across parts of South Asia and East Asia, with the Rossby wave potentially contributing to persistent enhanced rainfall across the equatorial Maritime Continent. Suppressed convection is favored to continue across much of the west-central Pacific, but Kelvin wave or MJO activity is favored to bring additional enhanced convection to the East Pacific and Central America. Renewed heatwave conditions are possible across parts of the U.S. Southwest. Please see the CPC U.S. Probabilistic Hazards Outlook for more information.

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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