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Global Tropics Benefits/Hazards
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Last Updated - 08.18.17 (Update)
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Global Tropics Hazards and Benefits Outlook Discussion |
| Last Updated: 08.18.17 |
Valid: 08.19.17 - 08.29.17 |
Updated discussion
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The MJO signal has completely broken down, with the velocity potential anomalies indicating a wavenumber 3 pattern, and both the Wheeler-Hendon and CPC Velocity Potential indices near zero amplitude. A Kelvin wave is moving across the eastern Pacific with another Kelvin wave in some analyses over the Maritime Continent. Some statistical tools and some dynamic models indicate an increasing signal in the MJO band over the Indian Ocean, with a signal moving eastward through Week-2.
Tropical Depression 13 formed over the eastern Pacific and Tropical Storm Harvey formed over the main development region of the Atlantic Basin since the last release on August 15. Through the remainder of Week-1, Tropical Storm Harvey is forecast to move across the Caribbean, while TD13 is likely to move out to sea. New tropical cyclone formations are likely over the Atlantic in the next 5 days, with 40-60 percent odds. Later, during days 5-11, tropical cyclone formation odds are again enhanced over the central Atlantic, well away from major land masses. The western Pacific is likely to be relatively suppressed for tropical cyclone development during days 5-11 period, with only a moderate chance of a tropical cyclone forming. A suppressed period would be consistent with an MJO band signal over the Indian Ocean. Over the eastern Pacific, a short lull in tropical cyclone activity, in the wake of TD13 is likely, with a potential return to an active period later in Week-2.
Enhanced tropical moisture is likely to impact Florida early next week. Some models also indicate moisture associated with Tropical Storm Harvey making its way across the Bay of Campeche and into Mexico, with potential impacts to Southern Texas, though uncertainty about that is high, as its well into next week.
--------------------- Previous discussion, from Aug 15, below -------------------------
The MJO remained weak during the past 7 days. Analysis of patterns in outgoing longwave radition plots indicates that two modes of variability, Equatorial Rossby Waves (ERW) and Kelvin Waves (KW), are major intraseasonal contributors to the patterns of tropical convection. Some methods of analysis are indicating the MJO building over the Indian Ocean, but that's likely an aliasing of the ERW. Going foward, most dynamical models indicate little to no MJO signal during the next 2 weeks, though the Canadian Ensemble and the GEFS do indicate a little strengthening over the Atlantic/African sector. All of the models do indicate eastward movement, across Africa toward the Indian Ocean, of whatever strength signal the respective model maintains. The predicted, generally weak MJO amplitudes suggest it will have limited influence.
During the past week, Hurricane Gert formed over the Atlantic, while Hurricane Franklin moved onshore in Mexico. Over the East Pacific, Tropical Storm Jova formed and dissipated with 2 days. The western Pacific remained active with Typhoon Banyan developing on 11 Aug. In the next week, the Atlantic Basin is likely to remain active with weak MJO support, a couple of robust African Easterly Waves, and the potential for a weak KW to enhance convection. This leads to multiple potential formations, with a secondary peak later in Week-1. Additionally, the Central Pacific Hurricane Center has a 50% chance of tropical cyclone formation indicated for the next 5 days. Over the West Pacific, formation odds are enhanced along 17N from about 135E to 160E. During Week-2, the central Pacific signal wanes, while the East Pacific becomes more favored, and the main development region of the Atlantic is likely to remain active. Tropical cyclone formation odds in the West Pacific wane from Week-1, and shift northwest to near Taiwan and extend into the South China Sea.
Given the lack of a robust MJO signal, forecasts for enhanced or suppressed tropical rainfall are based largely on dynamical model consensus and the likely progression of the ERW, KW, and weak MJO signal. Convection is likely to continue over southern India and portions of the Southeast Asia and the Maritime Continent, while some drying moves in along the equator near Sumatra. Some below average SSTs and dynamical model guidance favor below normal convection near the Date Line, which continues into Week-2. A cold front is likely to settle over southern Brazil.
During Week-2, model guidance has a large amount of uncertainty, and the largest signals are over the South China Sea and the Eastern Pacific. An amplified pattern is likely to remain over South America. The area of above average rains over southern India is likely to move northward, with some drying moving northward over central India. The ECMWF is more bullish on a developing MJO signal over the Indian Ocean in Week-2, while GEFS solutions depict drying near Sumatra and weak signals over the central Indian Ocean. They both agree on weak signals for wetness near the Maldives.
Forecasts over Africa are produced through 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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