There have been few changes made to the forecast since Tuesday, October 16. The MJO remains weak and model forecasts have not changed meaningfully over the past few days. The region of potential Week-1 TC genesis in the West Pacific has been trimmed a bit to better match the latest guidance. The forecast area for western Pacific TC genesis in Week-2 hasn't been modified since Tuesday, but the latest guidance suggests that the strongest threat for development in this area will be during the first day or two of Week-2 before disappearing quickly.
Tropical depression Twenty-Three-E formed in the East Pacific Friday morning (October 19). The National Hurricane Center predicts that it will reach tropical storm strength soon and track northwest over the next five days. There is another area of low pressure to the northwest of this storm, which looks ripe for development. This region has been added to the GTH forecast with a high confidence of development over the next five days.
---------- Original Discussion from October 16, 2018 is below: ----------
The subseasonal and low-frequency states of the equatorial Pacific are especially interesting this week. The MJO is allegedly in Phase 2, but has weakened substantially over the past few days. Dynamical guidance is in good agreement that it will continue to weaken over the next few days and then re-emerge in Phases 8/1 by the middle of Week-2. However, these forecasts are complicated by the developing El Nino in the Pacific.
El Nino development is usually characterized by convection shifting east of the Warm Pool, leading to positive OLR anomalies over the Maritime Continent/Warm Pool region. Anomalous low-level westerlies are also common in this area during an El Nino as the trade winds weaken (and sometimes reverse sign). The anomalous OLR and low-level winds are spatially and temporally similar to an MJO signal, which can project on to the RMM index. Even if an MJO manages to form under these conditions, the eastward shift in convection and warm SSTs that accompany an El Nino often makes it difficult for the MJO to remain convectively coupled as it passes the Maritime Continent. These similarities are likely to partially explain the models' inability to propagate the MJO through its full cycle. Since it's especially difficult to both evaluate the current state of the MJO and forecast the MJO into Week-2, it has taken a background role in this week's forecast.
There is a high risk of tropical cyclone formation in the West Pacific between 150-170E as multiple lows rotate clockwise around a fairly stationary high pressure system in the area. Both the GFS and ECMWF models suggest that at least one of these lows will develop into a TC in that region during both Week-1 and Week-2. Above-average rainfall is expected to along those tracks during both forecast weeks.
The Eastern Pacific remains active as well with high confidence of a tropical cyclone forming during Week-1 and a moderate confidence of formation during Week-2, especially towards the end of the period. Instablity in this region, and in the Gulf of Mexico, is expected to lead to significant rainfall during the forecast periods as well.
The evolution of El Nino, as well as the potential for MJO development during Week-2, favor below-average rainfall over the Maritime Continent and above-average rainfall in the western Indian Ocean.
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.