WASM- The WASM Regional Center is issuing a detailed seasonal bulletin for the 2024-2025 season for the Levant, Iraq, and the entire Arab region, based on data from WASM Regional Center's climate model which operates using flexible calibrated statistical similarity periods method, a new type of statistical processing characterized by superior accuracy exceeding the 75% threshold.
It is expected that the rainy season in Iraq and the Levant will be stronger than usual and cold during the rainy season, and the occurrence of severe cold waves during the winter season in certain periods cannot be ruled out. The autumn season is expected to witness rainy conditions at intervals that are sometimes slightly spaced, but these weather conditions will be strong overall.
Strong and cold rainy season|
The results indicate that the rainy season will be strong and cold, especially during the winter season, but it is expected that important rainy weather conditions will be delayed slightly in Iraq, with rainy periods during autumn being more spaced at times but heavy overall and coinciding with temperatures significantly below seasonal averages.
During the winter season, rainy conditions are expected to become more continuous and successive with the expectation of early cold waves compared to the usual situation, and the chances of snowfall increase in more than one period.
Rainfall rates|
It is expected that rainfall rates will be significant during the rainy season in large parts of Iraq, Syria, and Lebanon, especially during the winter season, with several heavy rainfall cases expected at the end of October and beginning of November and at slightly spaced intervals during November.
Iraq is expected to witness important and heavy rainfall cases at the end of October and during some periods in November, with the expectation of sharp cold waves occurring during January, and an increase in the chances of snowfall in some periods and may reach areas where snowfall is not usual, and important rainy conditions are delayed in parts of southern Iraq such as Basra and its surroundings until November.
The Levant is witnessing sharp activity of Mediterranean storm systems surging from the southeast of Italy or the Aegean Sea, especially during the winter season, with the expectation of experiencing several heavy rainy cases during the autumn season, and it is not expected that Syria and Lebanon will be affected by a delay in the rainy season, as they will experience several rainy weather conditions during some periods in October.
Temperatures|
Temperatures remain below seasonal averages for most of the rainy season, especially during the winter season and specifically during the first half of December, as well as during the second half of January and the first half of February.
The winter is expected to be severely cold during some periods, with increased chances of "dry" frost waves during some periods in January.
Short warm periods are likely during October and November that may occur between rainy conditions, but the dominant characteristic during the autumn period will be more stable and cold at the same time.
And an early cold wave during the first half of December cannot be ruled out, coinciding with rainy weather conditions throughout the regions.
Weather systems|
The Red Sea low dominates with a dry and warm extension over most areas of the Arabian Peninsula during October, and with the approach of Mediterranean lows (or Mediterranean storms) at the end of October, this is expected to increase the effectiveness of the Red Sea low, or there may be a direct impact sometimes during the last days of October and beginning of November.
Due to unusual atmospheric circulation, an acute extension of the Siberian high pressure system is expected to reach the north of the Arabian Sea region starting from the end of October and during the autumn period, and with the continuation of the Red Sea low extension toward western Saudi Arabia in a clear manner, this causes heavy rainfall cases at the end of October and beginning of November throughout western Arabian Peninsula, Jordan, and Palestine.
Due to the weakness of the subtropical jet stream significantly over the Mediterranean region and being opposed by the undulation of the polar jet stream over northwestern Europe during autumn, this causes easy flow of cold air through the middle and upper layers of the atmosphere toward the Arabian Peninsula and throughout the Mediterranean region.
During the winter season, the polar jet stream axis is expected to move toward the east of the Atlantic Ocean, causing a large bend in this current over the east and central Mediterranean and a direct surge of very cold air masses toward the region, and with the continuation of the weakness of the subtropical jet stream (a detailed scientific study will be dedicated to the reasons for the weakness of this stream), this will increase the chances of strong cold waves toward the Arabian Peninsula during the winter season, especially January, and the occurrence of strong early cold waves cannot be ruled out.
General situation of major climatic factors|
The Pacific Ocean is expected to experience a cold neutral state or a weak La Niña phenomenon (where the 3.4 region average is expected to reach -0.6 during October-November-December), the tropical Pacific Ocean region warms rapidly during December and January causing strange atmospheric circulation and major impact on the jet stream.
The tropical region of the Atlantic Ocean is expected to experience clear cooling during the upcoming rainy season, causing a significant change to jet streams in the Mediterranean region and the rest of the atmosphere.
These major climatic factors will significantly affect the circulation of tropical westward-moving waves – MJO, which will take a strange path over the tropical Pacific Ocean region and slower movement than usual in the tropical African region and parts of the Arabian Sea and Indian Ocean, causing a very significant impact on the subtropical jet stream and its significant weakening compared to the normal situation.
Weak North Atlantic storms and movement of their center axes toward the western Atlantic Ocean will result in another oscillation in the polar jet stream path and large bending of it over eastern European regions with expectations of a sharp weakening in its path during the winter season, especially with expected significant changes in the temperature of the northeastern Pacific Ocean region and near the western American coasts.
This system and the obvious changes in the atmosphere will result in strange paths for jet streams, long dry periods - very cold or warm - in higher latitude regions or mid-upper latitudes - and strong, sharp, and unusual Rossby waves in the atmosphere that particularly affect mid-lower latitudes and subtropical regions.
WASM Climate Model|
The model was run in a main cycle on 11-9-2024, with new data collection, calibration, and comparison with model results during the previous period, and a large and rare match was found reaching up to 80% during the previous period, which made us more confident in its results during the upcoming period.
This model operates using flexible calibration of statistical similarity periods method, or Analogue Calibration-Dynamic-Method, and it is a model that has been developed since 2018. It produces results at 200, 500, and 700 millibars levels in the atmosphere layers and operates in a different way and not entirely statistical, since statistical results are not accurate and give very random results that are temporally and spatially inaccurate. With the development of this model, we were able to overcome these statistical problems, and we were also able to achieve precise determination of temporally active periods reaching more than 90% in some periods, especially in autumn 2022, as well as autumn 2019, spring 2024, and summer 2023, when through this model we were also able to accurately determine the number of tropical storms expected to form in the Arabian Sea in autumn 2019.
WASM Center does not recommend relying on global climate models especially for our regions, as most Arab meteorological departments rely only on these models which reflects inaccurate results due to the lack of climate models specific to them.
The method of issuing long-range forecasts is extremely complex, as the behavior of the atmosphere is studied with utmost precision, and knowledge of the weather conditions it may lead to during the rainy seasons after running and calibrating the model to verify its results.
The accuracy of WASM climate model has increased from 60% to around 75% during the last season, and with the addition of many improvements and our ability to overcome statistical noise results responsible for errors that may occur in long-range forecasts.