Saudi Arabia and the Arab Gulf States| Detailed Seasonal Report for Season 2024-2025.. Slightly delayed start to the rainy season
WASM- WASM Regional Center issues the detailed seasonal report for the 2024-2025 season for the Kingdom of Saudi Arabia, the Arabian Peninsula region and the Arab Gulf states, based on data from the climate model of WASM Regional Center which operates using calibrated statistical similarity periods in a flexible manner, a new type of statistical processing characterized by exceptional accuracy exceeding 75%.
- Strong but delayed rainy season|
Results indicate that the rainy season will be strong, but will be slightly delayed compared to previous years, with its impact concentrated in vast parts of western and northern Saudi Arabia and the Red Sea coasts, starting from the end of October with intensification during November.
The rainy season is expected to be noticeably delayed in the central regions of the Kingdom, with an expected clear impact beginning in the second week of November, but it will continue throughout the rainy season on an intermittent basis.
Temperatures are expected to be slightly above seasonal averages across all regions during October-November, but will be noticeably below seasonal averages during December-January 2025.
- Rainfall rates|
Rainfall rates are expected to be significant during the WASM period in western and northern Saudi Arabia and Red Sea coasts despite the slight delay in the start of the WASM period, and rates will be substantial in central, northeastern regions, Hafar Al-Batin and Kuwait during November with an expected noticeably delayed start to the rainy season in those areas.
The southeastern areas of the Arabian Peninsula will experience long dry and warm periods, but the rainy season is expected to improve significantly and noticeably during the end of the winter season.
The Riyadh, Hafar Al-Batin and Kuwait region and surrounding areas are expected to witness little rainfall during October through the first half of November, with rainy weather conditions improving significantly during the second half of November and continuing intermittently throughout winter.
The Mecca and Medina region and their coasts will be affected by an excellent seasonal rainfall performance, expected to experience heavy rainy conditions during November, especially the second half of it, resulting in a significant increase in the likelihood of flash floods and strong rainy systems.
Al-Jouf, Hail, the Northern Borders region and Tabuk will begin to be affected by rainy conditions at the end of October, with a strong rainy event not ruled out at the end of October in Tabuk areas, its coasts and surrounding regions.
As for Qassim and north and west of the Riyadh region and surrounding areas, they will be affected by rainy conditions at the end of October and beginning of November and will continue intermittently throughout the rainy season.
- Temperatures|
Temperatures remain above seasonal averages across all regions (except northern Kingdom), declining noticeably to become below seasonal averages gradually during the second half of November.
Winter is expected to be extremely cold during some periods, especially during January, with increased chances of frost formation, freezing and snowfall in elevated areas of northern Kingdom.
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.
Due to unusual atmospheric circulation, a sharp extension of the Siberian high pressure system is expected to reach north of the Arabian Sea starting from the end of October, and during the WASM period, with the continuation of the Red Sea Low extension toward western Kingdom in a clear manner, this causes heavy rainy conditions at the end of October and beginning of November.
Due to the sharp weakening of the subtropical jet stream over the Mediterranean region and countered by the waviness of the polar jet stream over northwestern Europe during autumn, this causes the ease of cold air flow through the middle and upper layers of the atmosphere toward the Arabian Peninsula region and the entire Mediterranean.
During the winter season, the axis of the polar jet stream is expected to move toward the east Atlantic, causing a significant bend in this stream over the eastern and central Mediterranean and a direct thrust of very cold air masses toward the region, and with the continuation of the weakening of the subtropical jet stream (a detailed and comprehensive 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 winter especially January, with strong cold waves not ruled out in advance.
General situation of major climate factors|
The Pacific Ocean is expected to witness a cold balance state or a weak La Niña phenomenon (where the 3.4 region average will reach -0.6 during October-November-December), with tropical Pacific Ocean areas warming rapidly during December and January causing strange atmospheric circulation and significant impact on the jet stream.
The tropical Atlantic Ocean region is expected to witness clear cooling during the coming rainy season causing a significant change in jet stream circulation in the Mediterranean region and the rest of the atmosphere.
These major climate factors will significantly affect the circulation of tropical-westward propagating 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 areas of the Arabian Sea and Indian Ocean causing a very significant impact on the subtropical jet stream and significant weakening of it compared to the usual situation.
The weakness of North Atlantic storms and movement of their center axes toward the western Atlantic will result in another oscillation in the path of the polar jet stream and significant bending over eastern European regions with expected sharp weakening of its path during the winter season especially with expected significant changes to the temperature of the northeastern Pacific Ocean region and near the western American coasts.
This system and the clear changes in the atmosphere will result in strange paths for jet streams, long dry periods -extremely cold or warm- in higher latitude regions or middle-to-upper latitude regions- and strong, sharp and unusual Rossby waves in the atmosphere affecting particularly middle-to-lower latitudes and subtropical regions.
WASM Climate Model|
The model was run in a main cycle on 9-11-2024, with new data collection, calibration and comparison with model results during the previous period and found great and rare agreement reaching 80% during the previous period, which gave us greater confidence in its results for the upcoming period.
This model operates using the Analogue Calibration-Dynamic-Method, a flexible calibration for statistical similarity periods, a model being developed since 2018, and issues results at 200, 500 and 700 millibar levels in atmospheric layers, and operates in a different manner and not entirely statistical, as statistical results are not accurate and give very random results that are not accurate temporally and spatially, and with the development of this model we were able to overcome these statistical problems, and we were also able to achieve precise identification of temporally active periods reaching more than 90% in some periods especially in autumn 2022, and also autumn 2019 and spring 2024 and summer 2023, when through this model we were also able to precisely 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 their own climate models.
The method of issuing long-range forecasts is extremely complex, as the behavior of the atmosphere is studied with meticulous precision, and knowledge of weather conditions that may result from it during rainy seasons is obtained after running the model and calibrating it to ensure its results.
The accuracy of WASM's climate model has increased from 60% to around 75% during the last season and with the addition of many developments and our ability to overcome the results of statistical noise responsible for errors that may occur in long-range forecasts.