Since the original forecast release Tropical Storm 28W formed to the west of Guam and is forecast to track west-northwestward and slowly strengthen over the next 5 days. In addition, short-lived Tropical Depression 19 developed in the Gulf of California, and brought heavy rainfall to parts of Sonora and Sinaloa in Mexico. Remnant moisture of this system is forecast to feed into a frontal boundary sprawling across the Central US, leading to high confidence in above-normal rainfall for much of the Southern Plains during the next five days.
The National Hurricane Center (NHC) is anticipating a possible return to lively tropical cyclone (TC) activity in the Atlantic in the near future, as four areas are being monitored for development and two of these are featured in our updated forecast. Highest confidence exists for an area between the Azores and Bermuda where a non-tropical low pressure system is anticipated to develop subtropical or tropical characteristics around early next week, with a 70% chance of this occurring (high confidence). Another easterly wave is presently entering the tropical Atlantic near 10S, with a 60% chance of undergoing tropical cyclogenesis over the next 5 days (moderate confidence). Elsewhere, a remnant circulation from Florence is given a 30% chance of becoming a TC through the 26th, although it remains unclear if this system were to develop if it would be renamed or remain Florence. Lastly a weak low pressure area presently near 12N/50E is given a 10% chance of developing over the next 5 days due substantial wind shear and dry mid-latitude air in the vicinity of the circulation.
NHC is also monitoring two areas for development in the East Pacific. The first area is tied to a low pressure anticipated to form over the weekend between 10-15N and 100-110W, with a 50% chance of becoming a TC in the next 5 days (moderate confidence). Lastly a low pressure centered near 12N/125W is given a near 0% chance of becoming a TC due to persistent strong upper-level winds. Model guidance does suggest increased storminess throughout the Intertropical Convergence Zone (ITCZ) in the East Pacific over the next two weeks, tied to the anticipated emergence of the active phase of the Madden-Julian Oscillation in Phase 8. Model guidance indicates some of these systems may become weak TCs during the next two weeks, with substantial development appearing unlikely given enhanced westerly shear forecast across much of the Western Hemisphere. In Week-2 moderate confidence remains along the coast of Mexico for another system to possibly develop in the wake of the system NHC is monitoring in Week-1. TC tracking algorithms also suggest potential for TC development closer to the Central Pacific within the ITCZ near 10N between 130-145W.
Above- and below-normal rainfall areas are adjusted in the updated outlook to match the latest forecast TC tracks. The initial discussion from the original product release on Tuesday, September 18th follows below.
The MJO is currently weak, but model guidance is overwhelmingly favoring the MJO to strengthen and emerge in phases 8 or 1 by the beginning of Week-2. Support from the GEFS, CFS, ECMWF, and BOMM models suggest that this is a high confidence forecast and the MJO's climatological phase 8 state is the basis of the Week-2 GTH forecast.
There are three areas of potential TC development during the forecast period. Convection in the Bay of Bengal is likely to form a TC within the next few days. The GFS suggests this will occur more quickly than the ECMWF does, but both models agree that there will be a TC, forecast to track northwest, in the Bay of Bengal by Thursday.
There is an area of possible TC development in the West Pacific, just west of Guam and the Mariana Islands. Warm SSTs and low shear create a favorable environment for TC formation, but model guidance is uncertain about development potential. The deterministic GFS creates a TC just west of Guam, which it forecasts to track north and become caught in the extratropical flow before reaching Japan by the end of the Week-1 period. The ECMWF is similar, but forms a weaker TC further west. The GFS ensemble members are spread over about 20 degrees of longitude, suggesting significant positional uncertainty. The models remain split about the potential for TC development just west of the Week-1 region during the early part of Week-2, which we have included in our forecast. Interested parties are encouraged to monitor JTWC's updates for the latest information over the next few days.
Model guidance and the National Hurricane Center suggest that there is the potential for TC formation in the East Pacific just off the west coast of Central America during Week-1. This threat continues into Week-2, but is moved south and east. Models are split about whether a TC spins up in the East Pacific or Caribbean during Week-2, so we've posted a threat for both areas. We will monitor the situation and provide any necessary updates on Friday and again next Tuesday as we get closer to the potential formation period.
The MJO in phases 8 and 1 climatologically supports above-average rainfall in the west central Indian Ocean, which is included in our forecast and supported by ECMWF model guidance. The forecast MJO phase also supports below-average rainfall over the Maritime Continent.
Above-average rainfall south and west of Hawaii is expected during Week-1 as low pressure becomes wrapped up in the extra-tropical flow. Rainfall should fall back to climatological values as the MJO strengthens in phases 8/1 during Week-2.
Forecasts over Africa are made in consultation with the CPC international desk, and can represent local-scale conditions in addition to global-scale variability.
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.
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.
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.
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.