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ATTENTION:
The Climate Prediction Center is soliciting
comments from August 1, 2023 through January 31, 2024 on the implementation
of the Week 2
and experimental Week 3 Global Tropics Hazards Outlook.
Here is the Survey.
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GTH Outlook Map and Data
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Last Updated -
09/19/23
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GTH Outlook Discussion
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Last Updated -
09/19/23
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Valid -
09/27/23 - 10/10/23
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Following a brief uptick of the intraseasonal activity earlier this month, the Madden-Julian Oscillation (MJO) became largely disorganized, likely due to destructive interference with the ongoing El Nino, as well as other competing modes of variability in the tropics. This is reflected in the observed upper-level velocity potential anomaly fields, and the RMM index, which shows the MJO signal retreating westward across the Indian Ocean at a low amplitude during the past week. Looking ahead, however, there is a growing consensus in the forecast tools for a more coherent MJO reemerging across the global tropics. RMM forecasts generally favor the resumption of an continuous, eastward propagating signal, and although many ensemble means remain at fairly low amplitude in the dynamical models, there are several ensemble members that depict a potentially robust MJO event in the western Pacific during the outlook period. In addition, a healthier presentation of the MJO is revealed in the upper-level velocity potential anomaly forecasts. These favor the reemergence of a canonical wave-1 pattern, with the enhanced envelope shifting eastward across the Maritime Continent and into the western Pacific through early October. As a result, the MJO is likely to provide an increasing influence in the global tropics, where eventual constructive interference with the prevailing El Nino could help reinforce the low frequency response across the equatorial Pacific. A reorganizing MJO would also favor increasing chances for tropical cyclone (TC) development in the western Pacific, while lowering chances mainly throughout the western Hemisphere. However, the reduced TC genesis potential driven by the MJO over the eastern Pacific and Atlantic basins looks to be offset by their active TC climatologies, as well as forecast Kelvin wave activity which may help to incite formation.
During the last week, two TCs formed in the global tropics. In the Main Development Region (MDR), TC Nigel formed on 9/15 and has since strengthened to category 1 Hurricane over open waters of the central Atlantic. According to the National Hurricane Center (NHC), Nigel is expected to gradually intensity within a warm SST and light shear environment, but is forecast to recurve to the northeast and undergo extratropical transition, quickly becoming absorbed by an approaching mid-latitude trough later this week. In the eastern Pacific, TD13 formed on 9/19 near 15S/119W. This system is forecast to track to the northwest and reach Tropical Storm intensity in the next day or so, before becoming a remnant low over cooler waters to the north later this week.
For week-2, there is good agreement in the GEFS and ECMWF ensembles favoring an area of deepening low pressure over the South China and Philippine Seas likely tied to the enhanced phase of the MJO. Given the development of broad cyclonic flow favored in these models which may lead to one or more TCs forming, there is some uncertainty in regards to the details of timing and location of genesis, and a broad area of 40% chances is posted for the period. To the west, probabilistic TC tools have been consistent in depicting elevated probabilities for development over the Bay of Bengal. Though, confidence is tempered due to monsoonal shearing and a modestly active climatology heading into October, resulting in only 20% chances posted for the basin. While the suppressed phase of the MJO looks to inhibit TC development and bring drier than normal conditions over the tropical Americas, there are continued signals in the probabilistic TC tools to support 20% chances for TC development in the eastern Pacific. Similarly, 20% chances for TC development are also posted in the MDR associated with another tropical wave that is forecast to move off the coast of West Africa, and a predicted Kelvin wave passage in the basin.
By early October, extended range guidance favors strongly anomalous lower-level westerlies remaining entrenched across the South China and Philippine Seas (with anomalous easterlies to the north) to support the continuation of elevated chances (40%) for TC development. With the continued eastward propagation of the MJO forecast, the leading edge of the enhanced envelope could reach the eastern Pacific, which may lead to a more favorable environment for TC genesis over parts of the basin, and a broad area of 20% chances are issued. Across the Atlantic, climatology indicates a considerable shift of TC formations from the MDR to the Gulf of Mexico and Caribbean during early to mid October. However, there is little support for TC genesis here in the probabilistic tools, and the thinking is that any development potential will remain in the MDR where less shearing and near to above-normal precipitation is favored in the extended range guidance. Therefore, 20% chances are posted in the MDR from approximately 60W to 25W.
Forecasts for enhanced and suppressed rainfall based on a historical skill weighted blend of GEFS, ECMWF, CFS and Canadian ensemble forecasts, seasonal composites of El Nino, as well as composites of Maritime Continent and Western Pacific MJO events for weeks 2 and 3, respectively. For hazardous weather concerns in your area of the U.S. during the next two weeks, please refer to your local NWS office, the Medium Range Hazards Forecast produced by the Weather Prediction Center (WPC), and the CPC Week-2 Hazards Outlook. Forecasts made 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
