Over the prior week, minimal intraseasonal influences continued to be exhibited in both the Wheeler-Hendon and CPC velocity potential based indices. Instead, the low frequency background state appears to be driving the pattern throughout the tropics and subtropics, with the ongoing negative Indian Ocean Dipole (IOD) event and possibly developing La Nina yielding the most robust circulation responses in recent days. Outside of the Maritime Continent and West/Central Pacific, circulation anomalies are extremely benign, indicative of the weak forcing throughout the tropics aside from the aforementioned low frequency signals. Given this weakness and lack of robust signals in dynamical or statistical MJO guidance, continued weakness of intraseasonal activity is favored during the forecast period.
Tropical Storm 3 developed in the Bay of Bengal on October 25. Dynamical model guidance forecasts this system to track towards Andhra Pradesh in India, with limited intensification anticipated before landfall. In the East Pacific, Major Hurricane Seymour developed on October 23 near 13N/104W. As of 8 AM EDT on October 25, the National Hurricane Center estimates Seymour to have 100 kt winds, with some modest strengthening forecast today before subsequent rapid weakening anticipated within 48 hours. Dynamical model guidance expects Seymour to track west or northwestward into the Pacific as it weakens, but bring heavy rains along its track.
In the wake of Tropical Storm 3 in the Bay of Bengal, dynamical model guidance suggests a moderate risk of tropical cyclone (TC) development from a disturbance forecast to pass over the Malay Peninsula near the middle of Week-1. The GEFS suggests this TC may curve northward in the Bay of Bengal, with a forecast track that would approach Bangladesh late in Week-1. Regardless of cyclogenesis potential, heavy rains are likely with this system in the northern Bay of Bengal and adjacent coastal areas. Similarly, behind Hurricane Seymour in the East Pacific, there is a moderate chance of TC formation to the south/southwest of the Mexican states of Colima, Michoacan, and Guerrero during Week-1 where anomalously warm SSTs and low wind shear are forecast. Week-2 appears quiet for TC activity, aside from potential development in the West Pacific between approximately 160E and the antimeridan near 20N. Ensemble guidance suggests anomalously low surface pressure for this area in Week-2.
For Week-1 the greatest forecast confidence related to rainfall lies in areas impacted by low frequency variability. This includes enhanced precipitation over the Maritime Continent associated with the ongoing IOD event, enhanced rainfall south of Hawaii associated with anomalously warm SSTs, and suppressed rainfall to the east of the Maritime Continent due to persistent anomalous 200-hPa westerlies over the Indian Ocean that are focusing the subsidence response from Maritime Continent convection over this area. High confidence in above-average rains is also forecast with an anticipated cold front for the Caribbean, tropical Pacific moisture impacting California, and a northward surge of subtropical air into Colombia, Ecuador, and Peru. High confidence for below-average rainfall exists across southern India and Sri Lanka and portions of the southern Indian Ocean associated with the aforementioned strong westerlies aloft. Less confident regions for Week-1 are generally due to dynamical model consensus.
In Week-2 low frequency signals are expected to continue above-average rains over the Maritime Continent and south of Hawaii. Lesser confidence exists for the westerlies to persist across the Indian Ocean, resulting in the below-average rainfall region over Micronesia dropping to moderate confidence during Week-2. Remaining regions forecast for above- or below-average rains in Week-2 are due to dynamical model agreement. The anomalous precipitation forecast for the Bay of Bengal in Week-2 is reminiscent of a potential tropical cyclone track, and bears monitoring despite insufficient confidence to forecast an explicit TC hazard.
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.