The IRI has prepared this experimental Climate Outlook for North America for July 2001 - December 2001. Of relevance in the preparation of this outlook is the prediction of near-average to slightly warmer than average conditions in the eastern equatorial Pacific for the next 6 to 9 months. Currently the sea surface temperatures (SSTs) across much of the eastern and central equatorial are near their long-term average (SSTs) , although slightly lower than average SSTs have developed along the immediate western coast of South America and warmer than average SSTs persist in the extreme western part of the basin. Near neutral equatorial Pacific SST conditions are in effect for the first season of the forecast, July-August-September 2001, while during the second season, October-November-December 2001, they are expected to be slightly above average. The warmer than average SSTs that continue to dominate much of the Indian Ocean are expected to decrease slowly through the forecast period. The area of above-average temperature in the tropical south Atlantic Ocean is expected to persist through at least the first half of the forecast period.

METHODS -

This Outlook was prepared using the following procedures and information:

A) Coupled ocean-atmosphere model predictions of tropical Pacific SST covering the forecast period. Particularly heavy weighting has been given to predictions from the coupled model operated by the NOAA National Centers for Environmental Prediction, Climate Modeling Branch. This model suggests a continuation of near-average conditions during the first forecast season. The forecast for near-neutral conditions is consistent with some, but not all, numerical and statistical forecasts of central and eastern Pacific SSTs.

B) Forecasts of the tropical Indian ocean using a statistical model developed by the IRI.

C) Global atmospheric general circulation model (GCM) predictions of the atmospheric response to the present and predicted sea-surface temperature patterns.

D) Other sources of information include CPC ; >NASA's Seasonal to Interannual Prediction Project (GSFC-NASA).

The procedures, models, and data used to derive this Climate Outlook may be somewhat different from those used by the national meteorological services in the region. Thus, this product may differ from the official forecasts issued in those areas. The Climate Outlook for July - December 2001 is dependent on the accuracy of the SST predictions. For the tropical Pacific, these predictions can be expected to provide useful information, but there is some uncertainty concerning the evolution of SSTs. Spread in global SST predictions is a source of uncertainty in the Outlook provided here. Note that even if perfectly accurate SST forecasts were possible, there would still be uncertainty in the climate forecast due to chaotic internal variability of the atmosphere. These uncertainties are reflected in the probabilities given in the forecast.

It is stressed that the current status of seasonal-to-interannual climate forecasting allows prediction of spatial and temporal averages, and does not fully account for all factors that influence regional and national climate variability. This Outlook is relevant only to seasonal time scales and relatively large areas; local variations should be expected, and variations within the 3-month season should also be expected. For further information concerning this and other guidance products, users are strongly advised to contact their National Meteorological Services.

OUTLOOK -

This Outlook covers two seasons: July - September 2001 and October - December 2001. Maps are given showing tercile probabilities of precipitation and temperature. The maps for precipitation indicate the probabilities that the seasonal precipitation will fall into the wettest third of the years (top number), the middle third of the years (middle number), or the driest third of the years (bottom number). The color shading indicates the probability of the most dominant tercile -- that is, the tercile having the highest forecast probability. The color bar alongside the map defines these dominant tercile probability levels. The upper side of the color bar shows the colors used for increasingly strong probabilities when the dominant tercile is the above-normal tercile, while the lower side shows likewise for the below-normal tercile. The gray color indicates an enhanced probability for the near-normal tercile (nearly always limited to 40%). As before, numbers and their associated histograms show the probabilities of the three terciles. In areas with lots of spatial detail, there may not be sufficient room on the map, to allow histograms for each region. In those cases, some idea of the probabilities may be gained from the color alone. A qualitative outlook of climatology ("C") indicates that there is no basis for favoring any particular category. Areas that are marked by "D" represent regions experiencing their dry season (less than 15% of annual precipitation) and for which less than 5cm of precipitation typically occurs over the season. Otherwise, for example, in the case of July - September 2001 (Map A), there is a 25% probability that the precipitation will be in the wettest third of the years, a 35% chance it will be in the near-normal third of the years, and a 40% chance that the precipitation will be in the driest third of the years in much of the state of California in the U.S.

Maps of temperature show expected probabilities that the seasonal temperatures will fall into the warmest third of the years, the middle third of the years, or the coldest third of the years (Map A) . The numbers for each region on the temperature maps indicate the probabilities of temperatures to fall in each of the three categories, above-, near-, and below-normal.

An additional precipitation map is provided for the first season indicating probabilities for extreme precipitation anomalies. Extremes are defined as anomalies that fall within the top and bottom 15th percentile of the observed records. A priori, there is a 15% probability of being within the extremely wet category, and a 15% probability of being within the extremely dry category, leaving a 70% probability that the precipitation will not be extreme. The maps indicate areas of increased risk of extreme precipitation totals. Three levels of increased risk are defined: slightly enhanced risk, enhanced risk, and greatly enhanced risk. For slightly enhanced risk, there is a 25-40% probability that precipitation will be within the indicated extreme, i.e. wet or dry. This represents an approximate doubling of the climatological risk. For enhanced risk, there is a 40-50% probability that precipitation will be within the indicated extreme. This represents an approximate tripling of the climatological risk. For greatly enhanced risk, the probability that precipitation will be within the indicated extreme exceeds 50%, i.e. the indicated extreme is the most likely outcome. A similar map is provided in the first season indicating probabilities of extreme temperature anomalies.

Boundaries between sub-regions should be considered as transition zones, and their location considered to be only qualitatively correct.

July - September 2001:

PRECIPITATION

The following regions of enhanced probabilities of precipitation anomalies are indicated:

Slightly enhanced probabilities for above normal precipitation (25%-35%-40% and 30%-30%-40%) are indicated for western Alaska and the area in and around Bering Strait.

A region of slightly enhanced probability for below normal precipitation (40%-30%-30%) is forecast along much of the shoreline of Hudson Bay, Canada.

A greatly enhanced probability for below normal rainfall (50%-30%-20%) is forecast for the southern half of Baja California, Mexico. Weaker probabilities for below normal rainfall (45%-35%-20% and 40%-35%-25%) surround this region, including northwestern mainland Mexico and some of the western states of the U.S.

Enhanced probabilities for below normal rainfall (45%-30%-25%) are forecast for the Lesser Antilles in the Caribbean, with weaker probabilities for below normal rainfall (40%-30%-30%) in most of Puerto Rico, the Dominican Republic, Haiti, and the southeastern Bahamas.

A slightly enhanced probability for below normal rainfall (40%-35%-25%) is forecast for the Hawaiian Islands.

TEMPERATURE

The following regions of enhanced probabilities of temperature anomalies are indicated:

Slightly enhanced probabilities for above normal temperature (30%-30%-40%) are indicated for part of Greenland and Baffin Island in Canada.

A slightly enhanced probability for above normal temperature (25%-35%-40%) is forecast for a small region on the southern shore of Hudson Bay, Canada.

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for small portions of northern and central Alaska.

Enhanced probabilities for below normal temperature (45%-35%-20%) are forecast for Alaska's southern and western coasts, the Aleutian Islands, and in the vicinity of Bering Strait. Weaker probabilities for below normal temperature (40%-35%-20%) are indicated in adjoining peripheral regions, including coastal portions of the Alaska panhandle and a portion of southern Alaska inland from the coast.

A slightly enhanced probability for near normal temperature (30%-40%-30% and 35%-40%-25%) is forecast for parts of western Canada and parts of the panhandle of Alaska.

A slightly enhanced probability for below normal temperature (40%-35%-25%) is forecast for the central and southern California coast in the U.S. and for extreme northern Baja California in Mexico.

A slightly enhanced probability for above normal temperature (25%-35%-40%) is forecast for part of northern Mexico, part of the southern U.S., and a separate small portion of the state of Montana in the northern U.S.

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for part of the Maritime Provinces of southeastern Canada.

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for portions of the southeastern and mid-Atlantic parts of the U.S.

An enhanced probability for below normal temperature (45%-30%-25%) is forecast for parts of the Caribbean islands, including the Windward Islands, Puerto Rico, the south coast of western Cuba and the southern Bahamas. Weaker probabilities for below normal temperature (40%-35%-25%) surround these regions, including the tip of the Yucatan Peninsula of Mexico, Jamaica, most of Cuba, and some of the states of the southeastern and southern U.S. that border the Gulf of Mexico.

A greatly enhanced probability for below normal temperature (55%-30%-15%) is forecast for the Hawaiian Islands of the U.S.

Slightly enhanced probabilities for near normal temperature (25%-40%-35% or 35%-40%-25%) are forecast for most of southern Mexico, and all of the other countries of Latin America except for Guatemala.

October - December 2001:

PRECIPITATION

The following regions of enhanced probabilities of precipitation anomalies are indicated:

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for a portion of central and southwestern Canada.

Slightly enhanced probabilities for above normal precipitation (25%-35%-40%) are forecast for the southwestern U.S. and northwestern Mexico.

Slightly enhanced probabilities for below normal rainfall (40%-30%-30%) are forecast for part of the mid-Atlantic region of the eastern U.S.

Slightly enhanced probabilities for below normal and near normal rainfall (40%-40%-20%) are forecast for the southern half of Florida in the U.S. and much of the Bahamas.

TEMPERATURE

The following regions of enhanced probabilities of temperature anomalies are indicated:

Slightly enhanced probabilities for above normal temperature (25%-35%-40%) are forecast for a portion of western and central Canada, and part of the upper panhandle and southern coast of Alaska.

Slightly enhanced probabilities for below normal temperature (40%-35%-25%) are forecast for parts of eastern Canada, including the Maritime Provinces, and eastern Maine in the northeastern U.S.

Slightly enhanced probabilities for below normal temperature (40%-35%-25%) are forecast for most of the Aleutian Islands of Alaska.

An enhanced probability for above normal temperature (25%-30%-45%) is forecast for the Rocky Mountain region in the western U.S., as well as in a separate but associated small portion of western Mexico (20%-35%-45%). Weaker probabilities for above normal temperature (30%-30%-40%) surround and connect these two regions, including much of northern Mexico, and parts of the Great Basin and Great Plains regions of the U.S.

Slightly enhanced probabilities for near normal temperature (35%-40%-25%) are forecast for portions of the eastern U.S., paralleling the Appalachian Mountains.

An enhanced probability for below normal temperature (45%-35%-20%) is forecast for much of the central and western Caribbean region, including most of Cuba and the Bahamas. Weaker probabilities for below normal temperature (40%-40%-20%) surround this region, including the southeastern coast of the U.S. northward to the state of North Carolina, part of the Yucatan Peninsula of Mexico, northern Guatemala, most of Honduras, and the Caribbean islands of Jamaica, Haiti, Dominican Republic, Puerto Rico and the Lesser Antilles.

Slightly enhanced probabilities for near normal and above normal temperature (20%-40%-40%) are forecast for Costa Rica and Panama, extending southward into South America.

Slightly enhanced probabilities for near normal temperature (25%-40%-35%) are forecast for eastern Panama, extending southward into eastern and central Colombia of South America.

OBSERVED CLIMATOLOGY DATA for Jul-Aug-Sep and Oct-Nov-Dec

CLIMATOLOGICAL AVERAGE: Temperature Precipitation

TERCILE THRESHOLDS (33%-ile & 67%-ile): Temperature Precipitation

EXTREME THRESHOLDS (15%-ile & 85 %-ile): Temperature Precipitation

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