Author: gsjoko

On Tuesday afternoon, Senegal and Cabo Verde were finally clear of the bad weather from TS Rene. Flooding was the main impact across both countries from TS Rene. While the models had been suggesting some development, what manifested was not expected entirely. WRF had been suggesting the heaviest rains in Western Senegal. But the large vortex that emerged was shocking.

Satellite images suggested very heavy rain and the irain product suggested that rain was heavy and the WRF forecast model was suggesting up 12 inches of rain in some places. Below are videos from Senegal including Dakar, Mbour, Thies and Diamdiadio (western Senegal) that were sent to me from colleagues by whatsapp and taken by video from people in those regions.

You get the point, that the situation was serious and potentially life-threatening for people and animals. I am going to comb through the surface observations this morning to get a sense of what fell on the ground.

Cabo Verde

Tropical Depression 18 and then Tropical Storm Rene passed directly through the center of Cabo Verde. However, the reports are that it escaped heavy winds but there were reports of flooding in Santo Antao the more northwestern island which is very elevated. Satellite rainfall estimates suggest that Boa Vista, Sao Vicente and Santo Antao all received the highest rainfall. Of course, this all needs to be verified by ground measurements.

While, we can attribute this type of flooding to climate change, because of its association with a tropical disturbance, the atmosphere can hold more water vapor on a warmer planet. This will eventually manifest itself in heavier rainfall. Coastal West Africa and Cabo Verde are vulnerable now and definitely in the future unless CO2, Methane and other greenhouse gases are reduced. Because of these locations are situated near the Atlantic Ocean, disturbances have a moisture source to tap and as stated earlier the atmosphere can hold more water in a warmer world. There is evidence in the scientific literature that this is what is happening in West Africa, with heavier rainfall events over the last 2 decades. Future modeling studies by my colleague Dr. Bamba Sylla show that heavier rainfall events will manifest later this century with higher greenhouse gases.

The question that I have always struggled with is when does this happen?, is it gradual or is there a critical value with a tipping point?, after which, we never go back to earlier conditions. All of this feels like climate justice issue for the people in Africa who in general have historically contributed very little to the global burden of greenhouse gases. However, Africa’s its population increases and the use of fossil fuels increase it will contribute, which is why we need a different trajectory for the continent –> Solar energy, electric and hybrid cars and low-emission factories. The technology exists but is not readily made available to the continent and when it is, it is very expensive. Africa please unleash your innovative genius, because it is needed now!

In the next few hours, Cabo Verde will begin to experience the effects of Tropical Depression 18. This is earlier than expected based on earlier forecasts. The Islands of Boa Vista and Sal should expect heavy rains and winds that may reach tropical storm force values. It is likely that the entire country will see heavy rain from this storm and that the northern islands could be impacted the worst at this time.

The Early Track guidance suggests that the center of the storm will come closest to Boa Vista this afternoon and then tonight will move very close to Sao Nicolau, Sao Vicente, and Santo Antao. TD-18 will continue to strengthen as it cuts through the country and is likely to be a tropical storm when it reaches Boa Vista, Sal, Sao Nicolau, Sao Vicente and Santo Antao.

WRF 0000 SEPT 7 Output Analyses

The WRF simulation from last night provides some insight of what is possible over the next 18 hours

Initial Rains

The model suggest that the first rains will reach Sal and Boa Vista around 2000 UTC tonight. Satellite observations show that the first bands may arrive in the next few hours. I expect that when the main center arrives that the rain will be pretty heavy and extend southward to Santiago.

Sea Level Pressure

Based on the WRF forecast, the low will pass close to Boa Vista and Sal with tropical storm winds likely based on the latest NHC projection. During the night the low may pass over Sao Nicolau and then Sao Vicente and San Antao before continuing out to sea tomorrow afternoon. Because there are some high mountains, winds speeds and rains in these areas are likely to be enhanced.

Surface Wind Speeds.

Surface Winds speeds are likely to increase during the day as the storm deepens. Tropical Storm force winds can be expected over most of the Northern Islands, however these winds could be reached when rain bands pass by any part of the country.

WRF Rainfall Totals

Rainfall will be heaviest over the Eastern part of Cabo Verde tonight and then shift to Western Cabo Verde overnight. The 48 hour totals could reach 100-200 mm and could be higher in elevated regions. The rain will be intense when it does occur.

Key Takeaways

1. Make Final preparation for the storm now!! Charge your phones, fill your cars with gas and finish food shopping now. Touch based with loved ones before nightfall to make sure they are in good shape. Expect first rains in Sal, Boa Vista next few hours and poor conditions in about 5 hours.
2. Heavy rains could produce flash flooding, so be ready to move quickly if required to safety. Mountainous regions of Santiago, San Nicolau, Sao Vicente and Santo Antao are vulnerable to flash flooding tonight and tomorrow morning.
3. If you live near coastal zones, you will likely get some coastal flooding even for Islands to the south as a south fetch may produce heavy rains.
4. Some storm surge is expected Sao Nicolau, Sao Vicente and Santo Antao, if the storm passes the the south of these islands and even in the eastern parts of the islands based on the wind direction.
5. Please tune in to your local station to determine what is being done to protect people on your island and also know if there are local shelters.
6. Please pay attention to fallen trees and down electric power lines and wait until daylight tomorrow to assess the situation. Do not go out into the storm please.
7. Keep a cool head and prepare!!

Below are images from National Hurricane Center (1500 UTC)

When I woke up this morning, I did not expect to see an organized tropical disturbance, with clear cyclonic flow and banding. The last time that I saw this type of organization for such a large system was 2006, when TD-8 formed off the coast of Senegal during the NASA African Monsoon Multidisciplinary Analysis (NAMMA) campaign. However, that system was further south and many hundreds of miles more out to sea.

The global models are still not developing this system into a tropical cyclone near the coast, but I would say that the satellite observations should be enough to see the potential development. Ocean temperatures are above the threshold needed for tropical development (26 C) to occur and warm temperatures extend westward across the Atlantic to the United States.

The latest Sea Surface Temperature anomalies show that waters off the coast of Senegal are 1 Degree C- 1.8 F) above normal which may provide additional energy for the storm to develop.

Key Takeaways

• The tropical disturbance is organizing and is larger than suggested in model simulations. Over the next few hours, I feel that this will be an Invest and additional high-resolution hurricane models will focus on the system. For real-time images you can go to CIMSS http://tropic.ssec.wisc.edu/# as they are now following the system, just click on the invest (I).
• Senegal –
  • expect additional bands of heavy rain, today until the system moves away. Please careful for flash flooding and standing water on the roads.
  • A strong fetch from the south will occur over the next day and coastal flooding may become a real-possibility to many fishing communities and Dakar.
  • Pay attention to the national meteorological services, local TV, and Radio broadcast on weather conditions. If possible report your conditions via social media. Check-in with Raid on facebook at: La Météo Dakaroise de Riad
• Cabo Verde– You should prepare for:
  • several days of rain and wind, with the possibility of tropical-storm-force winds on some of the islands.
  • The seas will be rough and coastal flooding is also possible. Fishermen should be careful.
  • In areas that are flood-prone or have steep hills also prepare for possible flash flooding especially tomorrow and Tuesday. This includes the city of Praia where the houses tend to sit on steep hills.

Until later… Stay safe and will update this evening……

An infrared satellite view from EUMETSAT at 0200 UTC (10 PM) shows deep convection indicating that heavy rain is falling across Senegal, likely creating life-threatening flooding in some regions. Rainfall estimates from UIUC show that a 100 mm or (4 inches of rain) have fallen in some parts of Senegal.

The heavy rain is tied to a tropical disturbance that is expected to develop over the next few days and move across Cabo Verde.

Global Forecast models have had a time determining the strength of a possible disturbance, however they all agree that some type of disturbance is going to pass across Cabo Verde.

I have been using the Weather and Research Forecast model in research mode to determine the potential strength and path of the disturbance. Thus far, the model has been consistently developing a tropical storm that passes across Cabo Verde.

Sep 5 1200 UTC forecasts

Intensity and path of the forecasted storm

In the last model forecast from this afternoon, a tropical depression/storm develops but the path is further south and more likely to impact the island Santiago where the capital is located. The system continues to deepen as travels across Cabo Verde as it moves into Westward. For those of you who remember, Hurricane Florence which struck North Carolina took a similar path (not saying that is is likely as the storm has thousands of miles to travel to reach the US)

The forecast also suggests that much of Cabo Verde will receive winds that could be tropical depression to tropical storm force values especially on September 8. The wind field expands as it moves through Cabo Verde on September 8, with western islands likely to see the strongest winds as the storm deepens.

Heavy rain a major threat to Senegal and Cabo Verde.

Today’s 1200 UTC forecast shows that a large rain field will develop as the storm moves westward.

The heaviest rainfall would first impact Senegal on 5 and 6 September and then Cabo Verde on during the evening of 7 September. The predicted rain amounts would cause significant and widespread flooding if it occurred. The rainfall amounts were very high near Dakar on Saturday 05 September

The forecasts suggest that heavy rain will persist in Western Senegal on Sunday September 6 and as the storm moves westward will also produce high rainfall over Cabo Verde. The amounts foreasted in the model are beyond 10 inches for 4 days across Senegal and southern portions of Cabo Verde

Key Take Way Messages

1. If you live in Senegal, please protect yourself from heavy flooding and seek shelter if your life is threatened. Please be careful driving and do not drive across flooded roads.
2. Heavy rain is possible in Senegal until the storm pulls away from the coast on Sunday.
3. While we do not know the degree of the potential storm and its impacts on Cabo Verde, all models indicate that some type of disturbance will make its way across the islands from late Monday through midnight Tuesday and potentially early Wednesday. Better to be prepared.
4. A developing system that strengthens will pose some level of threat for coastal zones in Cabo Verde but it is still to early to tell the path of the storm or the strength of the winds which might produce surge and strong beach erosion. Fishermen and women will need to pay close attention to the news and the flag systems at local ports.
5. Low lying and flood prone areas should be identified over the next 36 hours in Cabo Verde.
6. Stay tuned to your local stations as the forecasts should get better as we get closer to the event.
7. If a strong storm does come, make sure that you are prepared to deal with potential power outages.
8. Until next time

A serious weather scenario is evolving in Senegal today and potentially over Cabo Verde at the beginning of next week. Unlike the powerful African Easterly Waves (AEWs) that typically pass at this time of year, these waves have been complex over the last week. The AEW that gave Cabo Verde good rain, is now moving towards the west and likely to become a named tropical cyclone in the next few days.

A new way is projected to develop today and will bring potentially heavy rains to Senegal and Guinea Bissau. It will then slowly move out over the Atlantic and deepen on Sunday and parts of Monday before impacting Cabo Verde. The WRF model runs, which are initialized by the US GFS model have been consistently developing what would be a tropical storm to impact Cabo Verde. It also suggest a second tropical cyclone will form later next week.

The forecast winds from yesterday’s model run are tropical storm force with the heaviest winds impacting the northern parts of Cabo Verde.

The simulated DBZ values suggest that rainfall amounts could be high through tomorrow noon in Senegal and the Gambia in coastal zone.

Is this Normal??

Typically this is the time of year when ocean temperatures are warmest and develop is possible. However, I feel that the northward position of the African Easterly Jet and its above normal strength is feeding energy (zonal kinetic) to disturbances off the coast of Senegal which would normally only amount to a minor disturbance. This has to be watched over the next 4-6 weeks

Key Takeaway:

1. If you live in Senegal, be prepared for heavy rain tonight and tomorrow
2. If you live in Cabo Verde…please pay attention to the news.
3. Stay Tuned… for the next forecast later today.

For the past day or so, a relatively stagnant pattern has developed near coastal West Africa with a traffic jam of disturbances (they are not moving westward as normal). As of today, weather disturbance over the ocean is expected to merge with the disturbance that just emerged off the coast of West Africa.

The weather system is then to pass over the country of Cabo Verde providing much-needed rain for farmers. However, the air is very unstable and likely to bring heavy rain to Senegal and Guinea Bissau tonight and tomorrow (Last night Senegal saw heavy rain from a Squall-line). This will be followed by another weather system that has the possibility of bringing more heavy rain to coastal West Africa. Some models have suggested that this second system will develop and maybe a tropical depression. At this point, it is still too early to tell but yesterday’s WRF model run forecasts heavy rain in Senegal and Guinea Bissau

The rain is particularly heavy along the coasts on 7,8 September because the surface low exits Senegals and then moves north, missing Cabo Verde. However, today, September 2nd Global forecasts are suggesting that the storm may pass over Cabo Verde. The high-resolution model simulations are still running as of this post. Here is the sea level pressure animation from yesterday.

Main take away point:

1. Heavy rain over Senegal, Guinea Bissau over the next 5 days
2. Possible disturbances to impact Cabo Verde tomorrow and Friday and potentially next Monday
3. Stay tuned