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GTH Outlook Map and Data
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Last Updated -
09/17/24
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GTH Outlook Discussion
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Last Updated -
09/17/24
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Valid -
09/25/24 - 10/08/24
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RMM observations show the MJO signal has struggled to fully propagate out of the Maritime Continent since late August. The stalling nature of the MJO signal appears to be related to continued Rossby wave activity in the western Pacific and Maritime Continent which has led to fluctuations of amplitude over this part of tropics in recent weeks. However, the signal has regained amplitude while resuming its eastward propagation more recently, and there is better confidence in the outlook that the MJO will continue to propagate into the Western Pacific and enter the Western Hemisphere during the next several weeks based on improved agreement in the RMM forecasts. While there remains some disagreement in regards to the strength and evolution of the MJO in the upper-level velocity potential forecasts among the models, objective wave filtering suggests that other modes of tropical variability are expected to be important contributors to Tropical Cyclone (TC) potential in the outlook. Specifically, strong Kelvin wave activity moving ahead of the enhanced convective MJO envelope looks to provide favorable conditions for tropical cyclogenesis over the tropical Americas, where continued signs of equatorial Rossby wave activity and a low frequency response aloft is expected to keep the western Pacific active through the end of September. Any reorganizing MJO is also expected to lead to an interruption of an enhanced trade regime over the equatorial Pacific, which may have implications on the favored transition to La Nina conditions later this fall.
During the past week, three TCs developed in the global tropics. In the eastern Pacific, TC Ileana formed on 9/12 and peaked at Tropical Storm intensity as it neared Los Cabos, Baja California bringing heavy precipitation to the region. Before dissipating on 9/15, TC Ileana also brought heavy precipitation and high winds to parts of western Mexico. After forming on 9/11 near 16N/28W in the Atlantic, TC Gordon tracked westward across the Main Development Region (MDR). Intensification had been kept at bay due to periods of high shear and dry air entrainment, and as a result, this system dissipated on 9/17. However, as of 1:30 pm EDT today, the NHC shows 40% chances of Gordon redeveloping, as its remnants enter a more favorable environment in the central Atlantic later this week. In the western Pacific, TC Pulasan formed on 9/16 near 18N/140E in the Philippine Sea, and the Joint Typhoon Warning Center (JTWC) expects this system to track northwestward into the East China Sea at Tropical Storm strength. Contrast to the slow moving TC Gordon in the Atlantic, the JTWC notes that constructive interference between a tropical upper tropospheric trough and a subtropical ridge is leading to an uncharacteristically high forward track speed of the system, where it is forecast to make landfall over eastern China in the next day or so. The JTWC is monitoring another tropical disturbance (98W) located over the northern Philippines with high chances of development, but has yet to form at the time of this writing.
Tied to the aforementioned Kelvin wave activity traversing the tropical Americas, there is good agreement in the models favoring the development of a band of anomalous lower-level westerlies extending from the south of Mexico into the western Caribbean and lower shear supportive of TC development. Based on good run-to-run continuity in both ensemble and deterministic solutions, and trends in the probabilistic TC genesis tools, 60% chances of TC formation are issued over the western Caribbean, with 40% chances covering both basins, and a broader 20% area extending into western Atlantic where tools also depict elevated signals during week-2. In the MDR, there is good support in the ensembles and probabilistic TC genesis tools favoring one or more easterly waves propagating off West Africa, and 40% chances are issued mainly east of 50W with a broad 20% area highlighted for much of the MDR for week-2. Inhibiting factors may still be periods of high dust and increased shear parts of the MDR, though the ITCZ looks to be in a more favorable position over the African Sahel. In the central Pacific, 20% chances are posted for week-2 approximately between 160W and 140W based on increased support in the ensembles for an area of deepening low pressure and probabilistic guidance. In the western Pacific, there is good agreement between GEFS and ECMWF favoring the persistence of anomalous lower-level westerlies extending from the South China Sea to the south of Japan. With several model solutions showing additional low pressure development, in the region 40% chances for development are issued. Further east, a separate area of 20% chances are also issued for the basin, where there is continued support in the probabilistic tools for development mainly east of the Marianas. Tied to Rossby wave activity predicted over eastern Indian Ocean and some support in the tools, 20% chances are also posted in the Bay of Bengal as this basin climatologically experiences its second mode of TC formations entering October.
Should the MJO remain coherent over the Western Hemisphere in October, this historically favors less favorable conditions for TC development in the western Pacific. However, 20% chances are issued over the South China and Philippines Seas during week-3 out of deference to the low frequency response favored in the velocity potential forecasts, as well as climatology. Conversely, a Western Hemisphere MJO would support an elevated potential for development in the Eastern Pacific, and 40% chances are issued to the south of Mexico, with 20% chances extending into parts of the Caribbean. While climatology continues to shift the TC formation potential more into the Caribbean, 20% chances are posted for a broad area in the MDR given modest support in the extended range tools.
Forecasts for enhanced and suppressed precipitation for weeks 2 and 3 are based on historical composites of Western Pacific and Western Hemisphere MJO events, anticipated TC tracks, and a skill weighted consensus of the CFS, GEFS, ECMWF, and ECCC model systems, with some consideration of ENSO cold phase composites. Tied to amplified 500-hPa ridging favored over much of North America, above-normal temperatures are likely throughout the western and northern CONUS during week-2. For hazardous weather concerns in your area during the next two weeks, please refer to your local NWS office, the Medium Range Hazards Forecast from the Weather Prediction Center (WPC), and the CPC Week-2 Hazards Outlook. Forecasts issued over Africa are made in coordination with the International Desk at CPC.
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Product Release Information
The Global Tropics Hazards 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 Google Meet) open to all stakeholders where the latest conditions and the newly
released outlook are shared with the opportunity to ask questions. Folks that are interested in learning more or attending these briefings should contact
Jon.Gottschalck@noaa.gov, Scott.Handel@noaa.gov, Adam.Allgood@noaa.gov and Nicholas.Novella@noaa.gov for the required information. Each weekly outlook and GTH release briefing is
Archived and available on the website.
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Product Description
The Global Tropics Hazards Outlook is a probabilistic forecast for areas with elevated probabilities for above- or below-median rainfall, above- or below-normal
temperatures and regions where tropical cyclogenesis is favored for the upcoming Week-2 and Week-3 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 brown respectively. Above (below) normal temperature forecast areas are depicted in orange and blue respectively. Favored areas for tropical
development are shown in red. Three probability intervals are indicated for precipitation and temperature which are set at 50, 65, and 80%, while the probability
intervals for tropical cyclone development are set at 20, 40, and 60%. 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.
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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.).
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Product Forecast Tools
The outlook maps are currently based on a number of forecast tools, many of which are objective and serve as an objective first guess. The final depiction is an
assessment of these objective forecast tools augmented by the forecaster when based on additional forecast information when appropriate to create the final product.
Forecast tools include MJO composites, empirical and dynamical based MJO, ERW and KW forecasts, and bias-corrected dynamical model guidance from a number of modeling systems.
Tropical cyclone areas are based on MJO composites and statistical and dynamical tropical cyclone forecast guidance products as well as raw model forecast guidance.
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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.
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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.
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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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Product Resources
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Feedback and Questions
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www.nws.noaa.gov
