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

Last Updated - 11.30.21 (Routine)


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Tropical Cyclone Formation KMZ / KML / SHP KMZ / KML / SHP
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Lower Tercile Precipitation KMZ / KML / SHP KMZ / KML / SHP
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Below Average Temperatures KMZ / KML / SHP KMZ / KML / SHP

Global Tropics Hazards and Benefits Outlook Discussion

Last Updated: 11.30.21 Valid: 12.01.21 - 12.14.21
Both the velocity potential based MJO and RMM indices continue to indicate that the MJO remains weak with enhanced convection anchored over the Maritime Continent consistent with the low frequency La Nina base state. However, recent combined infrared satellite and velocity potential spatial anomalies reveal the development of enhanced upper-level divergence and convection over the western Pacific, with more suppressed conditions emerging over Africa and the western Indian Ocean. Looking ahead, there is good agreement in the dynamical models continuing to favor renewed MJO activity, with most RMM forecasts showing the intraseasonal signal becoming more amplified and propagating eastward across the western Pacific during the next two weeks. Of note, there is a substantial increase in RMM2 values forecast over phase 6 during week-1, which is likely tied to development of anomalous lower-level westerlies which are favored to shift eastward from the Maritime Continent and supplant the enhanced trades that have persisted over the equatorial Pacific west of the Date Line.

Even with increased model support for this realization, there still remains uncertainty as to whether the MJO will maintain an organized structure given the likelihood of destructive interference with the base state, which is also evidenced by large ensemble spread in the forecasts through mid-December. Any coherence of the intraseasonal signal is more likely to manifest itself over the southern Hemisphere in the SPCZ region, which is reflected in the precipitation and upper-level velocity potential forecasts during the next two weeks. As such, tropical cyclone (TC) formation remains predominantly favored in the eastern Hemisphere, with more favorable conditions for TC development expected over the tropical southern Hemisphere during the outlook period. Downstream impacts over North America associated with Pacific MJO events during late boreal autumn historically favor more anomalous upper-level troughing (ridging) over the lower (higher) latitudes of the continent. However, this is at odds with the latest extended range guidance which depict more of a positive Arctic Oscillation (AO) pattern during the next two weeks. In light of this, and the aforementioned destructive interference with La Nina where MJO related convective anomalies are likely to be more focused in the southern Hemisphere, there remains high uncertainty regarding extratropical impacts over North America with the reemergence of the intraseasonal signal.

During the last week, one TC developed in the global tropics. Tropical Storm Nyatoh formed on 11/29 to the east of Mariana Islands and is forecast to rapidly intensity and curve under the influence of an approaching mid-latitude trough during the next few days. Beyond this time, unfavorable shear conditions are expected to quickly weaken the system, where it is forecast to eventually dissipate over open waters later this week. For week-1, there is good model agreement for TC formation in the Bay of Bengal associated with an area of low pressure shifting westward from the Gulf of Thailand, supportive of a high confidence area in the outlook. In the southern Indian Ocean, a moderate confidence area is issued to the south of Indonesia associated with another area of low pressure that is favored to strengthen in the deterministic solutions early in week-1. Despite less support from the ECMWF based guidance, there has been good run-to-run continuity from GEFS and GFS depicting an area of deepening low pressure in the Philippine Sea prompting a moderate confidence area in the region for week-2. In the South Pacific, several ECMWF and GEFS ensemble members show potential TC formation near the Coral Sea late in week-1 and into week-2. With Rossby wave activity, enhanced upper-level divergence, and reduced shearing conditions favored by the dynamical models over the region during the later period, a moderate confidence area is issued for week-2.

The precipitation outlook during the next two weeks is based on a consensus of GEFS, CFS, and ECMWF guidance, anticipated TC tracks, with some consideration given to composite precipitation anomalies of historic La Nina and Pacific MJO events. 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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Page last modified: 7-Sep-2021 3:09 PM EDT
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