The ongoing, strong El Nino continues to remain the major contributor to large scale tropical convective anomalies. The Wheeler-Hendon RMM MJO index indicates a slight increase in the amplitude of the index which is likely related to tropical cyclones, while the CPC MJO index based on 200-hpa Velocity Potential features a stationary pattern of upper-level divergence/convergence consistent with El Nino. Dynamical models and statistical tools favor a continued weak MJO signal during the next two weeks.
Tropical Storm Joaquin strengthened to a Category-4 Hurricane on October 1 as it remained nearly stationary over the central Bahamas. Although Joaquin moved northeast and well offshore of the U.S. East Coast, tropical moisture interacting with anomalous easterly flow and an upper-level trough across the Southeast resulted in widespread, torrential rainfall and flooding across the Carolinas during early October. Rainfall amounts in excess of 20 inches were observed across South Carolina.
Tropical Storm Oho developed to the southeast of Hawaii and is forecast to rapidly track north and east of the Hawaiian Islands during the next couple of days. Meanwhile, in the West Pacific, Typhoon Choi-wan originated near 20N-165E and turned north. Although it is expected to track east of Japan, it could bring heavy rainfall to Hokkaido in northern Japan. A Tropical Depression developed near 15N-125E and became Tropical Storm Mujigae before tracking west across Luzon, bringing heavy rainfall to the northern Philippines along its track. Tropical Storm Mujigae emerged across the South China Sea, where it rapidly strengthened and was classified as a Category-4 Typhoon, then made landfall a few hundred miles to the southwest of Hong Kong on October 4.
Anomalous rainfall during the next two weeks is based on El Nino and model guidance. Above-(below-) average rainfall is likely to persist across parts of the Central and East Pacific (Maritime Continent). During Week-1, above-average rainfall is favored along the expected tracks of tropical cyclones east of Hawaii and Japan. Above-average rainfall is likely across the upper and middle Rio Grande Valley as an upper-level low slowly tracks east. Ongoing convection and model guidance support above-average rainfall from southwest China west to the northern Bay of Bengal. This convection may be enhanced from the remnant moisture associated with the recent landfall of Typhoon Mujigae in southern China.
During Week-1, moderate confidence exists for tropical cyclone (TC) formation across the eastern Arabian Sea where a low-level circulation with convection is currently located. The GFS model indicates a slight decrease in surface pressure as this disturbance shifts north. The most likely area for TC development during the next two weeks is the West Pacific from 10-20N and near the Date Line west to 130E. Moderate confidence is depicted for weeks 1 and 2 due to uncertainty on the timing of TC development the West Pacific. Meanwhile, a tropical wave of low pressure is located 1000 miles southwest of the Baja California peninsula. Moderate confidence for TC development exists for this tropical wave in the East Pacific as it moves west during Week-1. Recent GFS model runs continue to favor TC development across the western Caribbean Sea late in Week-2. This is a region that typically becomes more active during October. However, high wind shear associated with the ongoing El Nino is expected to limit the chances for development across this region at this time.
Forecasts for Africa are done in collaboration with CPC's Africa Desk and based on model forecast guidance and regional scale anomaly features.
Product Release Information
The Global Tropics Hazards and Benefits Outlook is released once per week every Tuesday at 1530 UTC (1630 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.
The Global Tropics Hazards and Benefits Outlook is a forecast for areas with elevated odds for above- or below-median rainfall and regions where tropical cyclogenesis is favorable or unfavorable 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. 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.