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Global Tropics Benefits/Hazards
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Last Updated - 11.16.18 (Update)
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Global Tropics Hazards and Benefits Outlook Discussion |
| Last Updated: 11.16.18 |
Valid: 11.17.18 - 11.27.18 |
Updated discussion
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Through the past three days, the MJO signal has continued propagation into Phase 5, but seen a decrease in amplitude. Dynamical model guidance still supports eastward propagation, though guidance on the amplitude of the signal on the RMM index is varied. The GEFS predicts a resurgence of strength in the signal over the next few days, after a brief period of westward propgation, while the ECMWF maintains an amplitude near the edge of the unit circle. The signal is most robust in the upper-level wind field, which is leading the other components by a phase. Influences from the intraseasonal signal on the OLR field are likely to continue to dampen with the emerging base state.
Updates to the original forecast are minimal, especially since the Eastern Pacific and Atlantic basins seem to be winding down for the tropical cyclone season. No threats for TC formation are currently forecast for these reigons. For the Western Pacific, the possible TC formation east of the Philippines has been upgraded from moderate to high likelihood. The dynamical models remain in good agreement for a formation from this system. For Week-2, blocking at the higher latitudes in the North Atlantic are likely to lead to a series of shortwave troughs across the central north Pacific. There is moderate confidence that the above normal rainfall from Week-1 will continue into Week-2 for this region.
The discussion from the original forecast follows.
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The intraseasonal signal remained active through the past week, propagating through phase 3 and into phase 4. Kelvin wave activity likely contributed to the fast speed of this signal. In the OLR fields, the suppressed convective envelope shifted toward the Western Pacific, while the enhanced convection over the Indian Ocean expanded over the eastern Maritime Continent. Dynamical model forecasts of the RMM index over the next week show continued propagation into phase 5/6 and a rapid decay back inside the unit circle toward the end of Week-1, though statistical guidance is not as robust on the decay. The likelihood of a transition to El Nino has been upgraded to an 80% chance for the boreal winter. As the strength of this low frequency signal grows, the MJO signal is expected to become less dominant in the tropical circulation, especially as the suppressed convective envelope moves further into the Pacific and destructively interferes with the base state. A growing El Nino can bias the RMM index toward a Phase 7/8 structure, which may be what is being seen in the current model forecasts. As of this outlook, it is likely the MJO signal will dampen in amplitude over the next two weeks as it moves through Phases 5/6 in Week-1 and 7/8 in Week-2, though not as drastically as seen in the dynamical models.
The Indian Ocean basin has been active over the past week in the wake of the enhanced convective envelope of the MJO. Tropical Storm Bouchra formed on Nov 10 in the South Indian Ocean near 90 E and likely will be short lived. Tropical Storm Gaja, ongoing in the Bay of Bengal, is forecast to track eastward over the Indian peninsula through Week-1. As the MJO's suppressed convective envelope continues to expand westward toward the Maritime Continent, the Indian Ocean is forecast to be quiet through the next two weeks. The Atlantic and eastern Pacific basins are winding down their hurricane seasons as we approach the end of November. The National Hurricane Center is currently monitoring a disturbance in the western Caribbean, but have downgraded the likelihood of a tropical cyclone forming in the next 5 days to low. The only basin forecast to have any activity through the next two weeks is the western Pacific basin, while the enhanced convective envelope remains over the Maritime Continent and western Pacific. Model guidance shows agreement on possible tropical cyclone formation from a wave centered around 130 E; however, the forecast remains a moderate chance due to model run inconsistency.
Precipitation forecasts for Week-1 are mostly derived from impacts of the MJO or tropical cyclone activity. The Indian peninsula is expected to have above normal rainfall with the forecast track of Gaja. Another small region of enhanced precipitation is expected over Madagascar, where the forecast models show good agreement. With the MJO signal forecast to be in phases 5/6 in Week-1, suppressed convection is expected for the Indian Ocean, leading to below normal precipitation. Both the MJO signal and the developing base state support above normal precipitation along the equatorial Pacific, as well as parts of the western Pacific. Regardless if the tropical wave currently being monitored in the western Pacific basin forms into a closed low, it is still likely to cause above normal precipitation for the Philippines and the South China Sea. Model guidance, as well as MJO composites for phases 5/6, support below normal precipitation for Brazil.
For Week-2, suppressed convection is likely over the Maritime Continent, moving into the western Pacific as the MJO signal is forecast to further propagate into phases 7/8. Below normal precipitation is expected for parts of these regions, with high confidence over the western Maritime Continent and moderate further west, depending on how quickly the signal moves. In the southwestern Pacific, the above normal precipitation from Week-1 is expected to propagate further south. There is high confidence in the forecast for above normal precipitation along the equatorial eastern Pacific, supported by both the propagating MJO signal and the emerging base state. Brazil is likely to change to wetter than normal conditions with the impacts from enhanced convection due to the intraseasonal signal.
Forecasts over Africa are coordinated in consultation with CPCs international desk, and can represent local-scale conditions in addition to global-scale variability.
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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:
- 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.
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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