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Weeks 2-3 Global Tropics Hazards Outlook (GTH) |
For week-1 tropical cylone information and forecasts, please visit the National Hurricane Center and the Joint Typhoon Warning Center. For week-1 precipitation and temperature related products, please visit the Weather Prediction Center or refer to your local NWS office. |
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Last Updated - 09/24/24 | |||||||||||||||||||||||||||||||
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GTH Outlook Discussion |
Last Updated - 09/24/24 |
Valid - 10/02/24 - 10/15/24 |
Following a period of increased incoherence over the Maritime Continent, the RMM-based MJO index showed propagation over the Pacific during the past week, consistent with forecast guidance considered in the previous release of the Global Tropical Hazards Outlook. The inability for the signal to cross the Maritime Continent through much of early to mid September was due in part to the base state that continues to transition towards La Niña conditions, as well as alternatingly destructive and constructive interference with strong equatorial Rossby wave (ERW) activity over the far West Pacific and Maritime Continent. While east-central Pacific SSTs and upper-oceanic heat content continue to decline, the atmospheric response has been somewhat out of phase with a typical La Niña event, with increased suppression displaced to the east, over portions of the Western Hemisphere. This displaced response, coupled with enhanced West Pacific convection, helped to diminish tropical cyclone activity across the Atlantic basin during the climatological peak of hurricane season. During the next few weeks, dynamical model forecasts of the RMM index are in good agreement supporting continued eastward propagation of the MJO across the Western Hemisphere and Indian Ocean, followed by weakening and a potential quick return to the Maritime Continent. MJO events crossing the Indian Ocean typically result in reduced shear and low-level westerly winds across the Atlantic basin, which are favorable for tropical cyclone development. Additionally, the intraseasonal signal may help enhance the Central American Gyre (CAG) during much of the outlook period, which would promote increased convection and broad areas of low pressure across the far eastern Pacific, central America, and the western Caribbean. Therefore, the MJO is favored to play a substantial role in the overall evolution of the tropical convective pattern, primarily by reversing the previously persistent pattern of subsidence over the Western Hemisphere, yielding a window of favorability for late-season tropical cyclone development. Since September 18, three tropical cyclones developed globally. On September 22, Tropical Storm 17 formed over the Taiwan Strait immediately before moving ashore over mainland China. On September 23, Hurricane John formed over the East Pacific just south of Mexico, undergoing a remarkably rapid intensification to Category-3 intensity on the Saffir-Simpson scale just before landfall near Punta Maldonado. On September 24, Tropical Storm Helene formed over the far western Caribbean. Forecasts from the National Hurricane Center (NHC) bring Helene northward over the next several days, with a potential landfall over Florida’s Panhandle of Big Bend regions. Tropical Storm Helene also has the potential for rapid intensification, and current forecasts show the system at major hurricane intensity (Category-3 on the Saffir-Simpson scale) just prior to landfall. Please refer to the NHC for further updates on this system. During Week-2, low-level zonal westerlies are favored to develop across the far eastern Pacific and western Caribbean due to MJO activity, along with an enhanced CAG, support a continued active pattern, with additional tropical cyclone development possible over the East Pacific, southern Gulf of Mexico, and the western Caribbean. The highest probabilities for development extend from the Bay of Campeche eastward to the western Caribbean. Additionally, the Main Development Region (MDR) of the Atlantic is also favored to remain active, with tropical cyclogenesis favored in the region between the Lesser Antilles and the Cape Verde Islands. This enhanced activity may continue into Week-3, though dynamical model guidance becomes more diffuse. Additional development is possible over the far eastern Pacific, though the potential will decrease later into Week-3. A greater than 40-percent chance of formation is maintained across the Bay of Campeche and far western Caribbean during Week-3. Over the MDR, additional tropical cyclone development is possible, though tropical waves emerging during mid-October tend to take longer to develop. Elsewhere, a quieter pattern is favored for the West Pacific as the suppressed phase of the MJO overspreads the basin, though there is a slight chance for formations in the vicinity of Taiwan or north of the Philippines. Dynamical models indicate a potential for early season development across the south-central Indian Ocean, possibly in association with westerly wind bursts generated by MJO activity. During Week-3, dynamical models show a potential for development increasing over the Bay of Bengal as well. Forecasts for above- and below-normal precipitation are based on composites of MJO activity when the signal crosses the Indian Ocean, along with an anticipated continuation of enhanced convection over the Maritime Continent due to the low frequency base state. A reversal of suppressed conditions is favored for portions of the Western Hemisphere, while trade winds are favored to re-strengthen over the central Pacific after a period of disruption caused by MJO activity. 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. |
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. |
Product DescriptionThe 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. |
Product Physical BasisThe 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 ToolsThe 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. |
Product Purpose The product supports the NOAA mission in three primary ways:
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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. |
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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