Group work by: William AgyakwahJohn Nguyo Zablon ShilenjeNoah Eledi

Strong Winds; A Case Study in Nakuru, 13th March, 2013

Source jamaicansmusicz.com

Introduction

Wind is moving air caused by differences in air pressure resulting from differential heating from the sun. The greater the difference in pressure, the faster the air flows (Ahrens et, 2012)

On a global scale, the temperature difference between the tropics and the poles causes strong winds

Winds are commonly classified by their spatial scale, their speed, direction, e.t.c.

Measurement of wind speed and direction

Wind vanes Radio-sondes Beaufort scale Radar Satellite Aircraft Pilot ballons / optical theodolite

BeaufortWind scale speed in km/hr Description0 Under 1 Calm 1 1 - 5 Light air 2 6 - 11 Light breeze 3 12 - 19 Gentle breeze 4 20 - 28 Moderate breeze 5 29 - 38 Fresh breeze 6 39 - 49 Strong breeze 7 50 - 61 Near gale 8 62 - 74 Gale 9 75 - 88 Strong gale 10 89 - 102 Storm 11 103 - 117 Violent storm 12 Over 118 Hurricane

Forms of strong winds

NB: 30 knots = 55.56kph

Impact of strong winds

http://certifieddisaster.com

Strong winds are generally experienced in rift valley around January- March

There exists a channeling effect in the Rift valley which results in strong air current flow

On a much smaller scale, differential temperature gradients between land/lake and between mountains/valleys often create strong breezes.

Wind Characteristics in Kenya

Case Study:Nakuru, 13th March 2013

Heavy wind swept across Nakuru town on March 13th, 2013 afternoon and left traders and building owners counting their losses.

Several buildings and cars belonging to staff and individuals in and around the former provincial headquarters were destroyed as the winds blew away part of rooftops in several commercial buildings.

The strong winds swept in from the northern side of Nakuru town forcing traders, business operators and retailers to scamper for their safety as it blew away anything on its path.

Several individuals were seriously injured in the tragedy.

Nakuru town has been experiencing persistent windy periods during the dry season.

Residents feared that worse incidents may occur in future and called on relevant authorities to intervene and establish mechanisms that could forestall such destruction.

(KTN Television, 2013)

Case Study Objective

The study inquires whether it is possible for the Kenya Meteorological Service to forecast strong winds in Kenya

Climatology of Nakuru

Located at Lat 00, 16’S and Lon 360, 06’E

Elevation 1,901m AMSL

Nakuru has a warm and temperate climate

Average temperature 17.5 oC

Population 1,603,325 persons

Area 7,510 km²

(source; KBS, 2010)

Damage caused by Strong Winds in Nakuru on 13 March, 2013

Play Video (courtesy of KTN Television)

The roofs of classrooms were blown off in the afternoon incident that disrupted learning activities at the school.

A section of the walls also collapsed on impact during the afternoon incident.

Observed METARS at Nakuru

METAR HKNK 1000Z 03O20KT 9/9 SCTO32 29/04 =METAR HKNK 1100Z 03O10KT 9/9 SCTO32 29/03 =METAR HKNK 1200Z 06O10KT 9/9 SCTO32 29/05 =METAR HKNK 1300Z 03O10KT 9/9 FEWO32CB BKNO32 31/05 =METAR HKNK 1400Z 0103OKT 9/9 FEWO29CB BKN030 29/02 =METAR HKKK 1500Z 01O10KT 9/9 FEWO28CB BKN030 25/10 =

Note change in wind speed, temperature & CB

Dominant wind direction was North North Easterlies (NNE)

Recall eyewitness account in clip, that strong winds swept in from the northern side of Nakuru

Wind roses for Nakuru between 1000 - 1700Z on 13th March, 2013

Data source; KMS

No satellite image as we were not able to retrieve any

Our View On The Case Study Question

Is possible for the Kenya Meteorological Service to forecast strong winds?.

Yes, it is likely to forecast strong winds but challenging to a forecaster with limited observational data and other forecasting tools e.g. high resolution numerical models

Conclusion & Recommendation

Strong wind are both disastrous and beneficial

The strongest gap winds are typically in the gap exit region

We need more monitoring instruments in Nakuru area

References Materials

Ahrens, C. Donald. Meteorology today: an introduction to weather, climate, and the environment. Cengage Learning, 2012.

Kenya National Bureau of Statistics, 2010

Kenya Television Network broadcasts, 2013

Kenya Meteorological Service, dataset

The End

Thank you