The amplitude of the MJO signal decreased this week according to the RMM index, while the CPC index based on the Velocity Potential field also indicated a weakening trend. Therefore, the MJO is not expected to significantly influence anomalous convection across the global tropics during the outlook period. The evolving base state and warmer-than-normal SSTs are likely to be the primary contributors.
Since a stationary front is expected to shift southeast during the next 24 hours, much drier weather is expected for the Florida Keys and south Florida. Therefore, the coverage of above-average rainfall is reduced to include only the southern Bahamas, Cuba, and the Cayman Islands from October 25-28. Redevelopment of Tropical Depression Nine in the Caribbean Sea is unlikely due to rising surface pressures in this region. Meanwhile, as of October 24, a trough of low pressure to the south of the Gulf of Tehuantepec is producing a disorganized area of convection. Conditions are forecast to become more conducive for tropical cyclone (TC) development. The latest model guidance closes off a surface low across the East Pacific during the next few days. Therefore, confidence is high that a TC develops in this region from Oct 25-28 which is consistent with the NHC update at 2pm EDT on Friday, Oct 24. Model guidance remains consistent that above-average rainfall persists across the East Pacific into the beginning of November.
As of October 24 at 11pm HST, Tropical Storm Ana, near 28N-170W, is forecast to become extratropical by Monday as it accelerates northeastward. Above-average rainfall is depicted on the map along its track. Extratropical Ana is anticipated to be absorbed by a strong extratropical low approaching British Columbia on October 27. Moisture associated with the remnants of Ana has the potential to briefly enhance precipitation amounts across British Columbia and the Pacific Northwest.
Elsewhere, no major changes were made to the previous outlook issued on October 21.
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Some observations indicate a more coherent MJO signal during the past week. The CPC Velocity Potential based index indicates a Wave-1 structure but the fast propagation resembles a more transient atmospheric Kelvin Wave. The RMM index had an increase in amplitude with eastward propagation from the Americas to Africa. Dynamical and statistical models generally agree that a long-lived MJO signal is not likely with Kelvin Wave activity influencing anomalous convection across the global tropics during Week-1.
Gonzalo peaked as a Category-4 Hurricane with maximum sustained winds of 145 mph on October 16 before making landfall over Bermuda on October 17 as a Category-2 Hurricane with maximum sustained winds of 110 mph. Gonzalo was the second tropical cyclone to strike Bermuda in less than one week. Although Hurricane Ana tracked south of Hawaii, it resulted in heavy rainfall amounts including locally more than 11 inches across the Big Island and Oahu. Following a very active period of tropical cyclones including a pair Super Typhoons, no tropical cyclones formed during the past week over the West Pacific.
A stationary front is likely to remain the focus for heavy rainfall from the Bay of Campeche and Yucatan Peninsula east to the Bahamas and western Cuba. An area of low pressure currently in the southern Bay of Campeche could become a tropical cyclone before interacting with the stationary front later this week. Suppressed convection is expected to persist for coastal southern Brazil. A Kelvin wave and warm SSTs favor enhanced rainfall along and to the south of the equatorial Pacific east of New Guinea . The suppressed phase of the Kelvin Wave is anticipated to result in below-average rainfall for parts of the Maritime Continent. The enhanced rainfall areas depicted across the Arabian Sea and southern Indian Ocean are based on model guidance and warm SSTs. A moderate confidence for tropical cyclone development is posted for the southern Indian Ocean due to the likelihood of enhanced convection is this region and climatology. Anomalous low-level convergence is expected to enhance rainfall across parts of equatorial Africa.
During Week-2, confidence is relatively low due to an anticipated weak MJO and conflicting signals between the CFS and ECMWF models. Above-average rainfall is favored to continue east of New Guinea due to the base state with warm SSTs. Today's model solutions remain consistent with above-average rainfall for parts of the Indian Ocean and East Pacific. The GFS model indicates the potential for a late season tropical cyclone in the East Pacific, but chances are too low at this time to warrant a depiction on the map.
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.