Numerous modes of tropical variability were at play across the Indian Ocean during the past week, resulting in a complicated perspective. First, the ongoing Indian Ocean Dipole event remained anchored across the basin, although sea surface temperature observations show a continued weakening from its record weekly values. Constructive interference occurred with the IOD-driven enhanced convection across the western Indian Ocean, a pair of equatorial Rossby waves in both hemispheres, and the enhanced phase of the Madden-Julian Oscillation (MJO). On top of this, a Kelvin wave passed through the region in late November, further encouraging anomalous convection over the Arabian Sea and southwestern Indian Ocean. The net result was a strong east-west dipole of enhanced (suppressed) convection over the western Indian Ocean (Maritime Continent), with some displacement of the suppressed convection into the Southern Hemisphere that may have been tied to cross-equatorial outflow from Typhoon Kammuri in the West Pacific. The RMM index perspective of these interactions was a counterclockwise loop in Phase 2 at an amplitude near 1, with some signs of renewed eastward propagation of the intraseasonal envelope. Model guidance continues this eastward propagation for the next two weeks toward the Maritime Continent, but is divided over how quickly this occurs and how robust the amplitude of the event would be. The forecast here generally favors MJO Phase-2 during Week-1 and Phase 3-4 during Week-2, with the caveat that Week-2 would see destructive interference with IOD that reduces confidence some at that forecast lead.
Tropical Storm Six was one of two tropical cyclones (TCs) to develop over the past week. This system formed east of the Horn of Africa on the 3rd and is forecast to remain at tropical storm intensity and track westward into Somalia by late in the first week of December. Later on the 3rd, Tropical Storm Seven developed in the Arabian Sea with the latest JTWC foreacst having the system maintain marginal tropical storm strength while tracking west-northwestward over the next several days. While not forming last week, Typhoon Kammuri made landfall in the Philippines on the 2nd of December as a Category 3 storm while dropping 150-250 mm of rainfall and causing at least four fatalities.
The Joint Typhoon Warning Center (JTWC) is presently monitoring two disturbances for TC formation potential. The first of these is located north-northeast of Madagascar, with JTWC giving the system a medium chance of becoming a TC in the next 24 hours. Model guidance consistently strengthens the system to below 980-hPa over the next several days, resulting in high confidence of its formation during Week-1 in this outlook. Elsewhere, a circulation south of the Marianas is given a low chance of becoming a TC in the next 24 hours by JTWC. Model guidance brings this system east of the Philippines over the course of the next week with some modest intensification, resulting in moderate confidence for a TC developing over the next week. Beyond those two systems, model guidance develops a circulation west of the Maldives by Friday and forecasts gradual intensification of the low as it tracks toward the Gulf of Aden which results in moderate confidence of tropical cyclogenesis during Week-1. A second TC may also develop during Week-1 east of the system in the southwestern Indian Ocean, resulting in another moderate confidence of TC formation region. Lastly, Rossby wave activity continues to be forecast east of the Philippines during Week-2, resulting in moderate confidence for tropical cyclogenesis across a slightly eastward shifted region relative to that of Week-1.
High confidence for above-normal precipitation exists during Week-1 in association with tracks from ongoing or anticipated TCs in the Indian Ocean and West Pacific, while frontal activity during Week-1 is anticipated to miss the Southeast U.S., yielding high confidence for below-normal precipitation. The anticipated eastward propagation of the MJO and continued Rossby wave activity result in a continuation of high confidence for above-normal rainfall over much of the Indian Ocean during Week-2. Moderate confidence for above-normal precipitation across much of the Pacific near 10N is tied to the low frequency state, forecast Rossby wave activity, and MJO composites for Phases 3 and 4. Remaining precipitation forecasts are tied to dynamical model consensus of the CFS, GFS, and ECMWF ensembles. Moderate confidence for above-normal temperatures across portions of Australia during the next two weeks is in line with the latest outlooks from the Australian Bureau of Meteorology and CPC's probabilistic extremes guidance from the GEFS and ECMWF.
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.
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.
The product supports the NOAA mission in three primary ways:
- 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
- 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)
- Support various sectors of the U.S. economy (finance, energy, agriculture, water resource management) that have foreign interests.
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.