Printer Friendly

Weather Patterns

Clarification Statement: Examples of data at this grade level could include average temperature, precipitation, and wind direction.

 

Assessment Boundary: Assessment of graphical displays is limited to pictographs and bar graphs. Assessment does not include climate change.

These activities build on the content below.

Hahai no ka ua i ka ululāʻau.

Rains always follow the forest.

The rains are attracted to forest trees.

Knowing this, Hawaiians hewed only the trees that were needed.

—ʻŌlelo Noʻeau #405, Mary Kawena Pukui


Rain Around the Islands

Rain in Hawaiʻi is location specific. Some areas are very dry, and others are almost always rainy. The Western (leeward) sides of the islands tend to be drier than the Eastern (windward) sides (Fig. 1). The dryest location in Hawaiʻi is the summit of Mauna Kea, Hawaiʻi Island, which gets less than 10 inches of rain per year. On the other hand, the windward slope of Haleakalā, Maui, gets more than 400 inches of rain each year. 

<p>FIg. 1. Rainfall varies between the windward and leeward sides of the Hawaiian Islands.&nbsp;</p><br />

Most of the rain in Hawaiʻi is caused by winds interacting with the mountains (Fig. 2). The normal trade wind direction is East-Northeast. Therefore, the average rainfall for the East facing sides of the islands is higher than for the West facing sides. General rainfall patterns occur in the following manner:

  1. As the trade winds contact the windward mountains, air is forced upward.
  2. Rising air cools because of colder temperatures in the upper atmosphere.
  3. As the air cools, water vapor in the air condenses on small particles called condensation nuclei to form clouds, water droplets, and rain. 
  4. Plants capture rain and help it to slowly move through the ground.
  5. Once the water is released from the air, there is less water to fall on the other side of the mountain, or leeward side.


The mountains bring the rain by physically pushing air up and cooling it. But, the forest is needed to capture the rain. The complex, multi-layered nature of the native, Hawaiian forests are very good at capturing water from clouds and from rain. Humans have cleared land for grazing, harvested forests for trees, and allowed invasive animals and plants to destroy the native forests. Efforts are now underway to restore native forests in order to help cature fresh water and help to recharge underground aquifers.


<p>Fig. 2. The patterns of rainfall around the Hawaiian Islands is due in large part to the interaction of the winds and landscape.&nbsp;</p><br />


Weather

<p>Fig 3. A rainbow forms over the big island of Hawai'i after a rain storm passes through.&nbsp;</p>

Weather is all around us (Fig. 3). It has a large effect on our daily lives. The weather affects how and where we live, what we do each day, what we wear, and what we eat. Weather is made up of many different atmospheric factors, like:

Meteorology is the study of weather. A person who studies weather is called a meteorologist. Meteorologists make weather predictions based on the interactions of atmospheric factors. 


Climate

<p>Fig. 4. Climate represents weather conditions over long periods of time.</p>

Climate is a term used to describe average weather conditions (Fig. 4), in a particular place, over a long period of time. The weather changes from day to day, but climate changes take place over many years (for example, more than 30 years). This means that, even though it may rain sometimes in the desert, on average the climate is hot and dry. The Antarctic has a very cold and dry climate. Tropical places, like Hawai‘i, have warm, humid climates. 


The Water Cycle

The water cycle is the recylcying of water through evaporation, transpiration, and precipitation (Fig. 5). During rainy periods, plants, soils, rivers, and lakes take up water.

Periods of hot, dry weather can lead to water evaporation and transpiration. Plants and soil dry out. Streams and rivers shrink to lower water levels.

But, over the course of several years, a balance occurs in the water cycle so the amount of water entering the system is equal to the amount exiting. This balance, or equilibrium, in the hydrologic cycle helps stabilize the climate.


<p>Fig. 5. The water cycle has a big influence on weather and climate.&nbsp;</p><br />


Climate is affected by the natural fluctuation of the balance of water entering and exiting the system on a global scale. The availability of water depends on the ocean and the atmosphere—as well as on large freshwater lakes and glaciers. Natural hazards like floods, droughts, sea level rise, and elevated sea surface temperature affect daily weather events, but they can also have long-term impacts on the climate.


Climate Changes

<p>Fig. 6. A flooded intersection (near the corner of Keeaumoku &amp; Makaloa Streets in Honolulu) reveals the potential dangers of excess rain. This photo was taken in 2006.</p>

Scientists are studying how different factors impact the climate. Scientists also observe local weather for patterns that can be predicted on reliable timescales. The majority of climate scientists agree that one of the biggest threats to our Earth is the rapid, global climate change taking place as a result of human influence. The energy and resources used by humans are converted into gases that change the chemistry of the atmosphere. Climate change can alter the water cycle by increasing (1) the likelihood of floods in usually dry regions and (2) droughts in historically wet regions (Fig. 6).

 

As a result of Earth's warming climate, many of the world’s glaciers are melting. These melting glaciers can significantly raise the water level in the ocean (see the grade 5 activity on rising sea levels!). The warming climate also changes weather patterns in some areas, making weather harder to predict and ultimately producing more severe weather as a result. In tropical regions such as Hawai‘i, global climate change can contribute to a rise in sea surface temperatures. This rise in temperature is important because even small increases can have big effects on coral reefs, causing bleaching that eventually can lead to the death of both corals and the associated ecosystems.


Weather Vocabulary

  • Air Pressure: the weight of the air on the earth’s surface; at sea level, the air pressure is higher compared to high up on the tops of mountains because there is less air between the atmosphere and the tops of mountains than sea level
  • Atmosphere: the mass of air surrounding the Earth
  • Climate: the average weather conditions over a period of years
  • Clouds: visible masses of condensed water vapor suspended in the atmosphere
  • Condensation: the transformation of water vapor back into liquid water by cooling
  • Condensation nuclei: small particles (typically 0.2 µm, or 1/100th the size of a cloud droplet) on which water vapor condenses. Water requires a non-gaseous surface to make the transition from a vapour to a liquid; this process is called condensation.
  • Evaporation: the process in which the sun heats up water in rivers or lakes or the ocean and turns it into vapor; the water vapor goes into the air where it becomes a cloud
  • Fog: water vapor that is suspended in the lower altitudes; similar to a cloud except for its proximity to the ground
  • Ho‘oilo: the Hawaiian term for a wet season
  • Humidity: the measure of how much water vapor is in the air 
  • Hydrologic cycle: the cyclic transfer of water among the oceans, land and atmosphere.
  • Kau: the Hawaiian term for summer
  • Kona storm: an unusual winter storm, often lasting days with potentially heavy rain and high winds
  • Kona weather: warm, humid, calm weather with typical winds from southwest
  • Leeward: the side of an island that is downwind and is usually dry
  • Makai: the Hawaiian term for ocean side, or an area located next to an ocean
  • Mauka: the Hawaiian term for mountains, or an area located next to the mountains
  • Meteorology: the science that studies the atmosphere and its phenomena in relation to the weather and weather forecasting
  • Precipitation: rain, hail, or snow falling from the clouds due to the condensation of water
  • Transpiration: the process in which water evaporates through pores in the leaves of plants
  • Weather: the state of the atmosphere in regard to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness. It is the day-to-day conditions of the atmosphere
  • Wind: the movement of air; both direction and speed are measured for weather observations
  • Windward: the side of an island that is upwind and is usually wet

 

Table of Contents:

Representative Image: 
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.