Hawaii Weather Patterns

Geography 101 Lab

WARNING! This lab requires that you complete four days of weather observations so you must begin at least four days before the final deadline.

Writeup Instructions: (4 Steps) For this lab, the writeup is less structured than previous labs. Follow the instructions for each Step. Enter your answers under Lab Report 7 in the Submit Labs area. Do NOT email me your answers. I highly recommend that you record your answers using a word processing program, save, and then cut and paste into the answer area.

Purpose: Become familiar with the basic pressure system configurations near the Hawaiian Islands and the weather they bring, learn to recognize these patterns on a day to day basis using the synoptic weather forecast, and relate the synoptic forecast to the local weather in your area.

In this lab, we link abstract weather concepts, daily weather service forecasts, and your own personal observations of the weather actually occurring. This exercise has several objectives:

• understand the physical relationships between pressure systems and weather
• learn the basic weather patterns that are most common in Hawaii
• relate abstract weather model concepts to the weather actually occurring

The lab has three components:

1. study and summarize the material provided explaining the basic weather patterns
2. record the official synoptic forecast for the Hawaiian Islands for four days
3. record your own observations of the weather occurring where you are located each day for four days

Definitions:

• Circulation: large-scale wind pattern
• Front: the boundary between warm and cold air masses
• Kona Weather: warm, humid, calm weather with typical winds from southwest
• Kona Storm: an unusual winter storm, often lasting days with potentially heavy rain and high winds
• Instability: atmospheric conditions favorable for rising air and deep cloud formation
• Inversion: a layer in the atmosphere where temperature increases with height. Common over Hawaii near 6000 to 8000 feet altitude.
• Pressure Gradient: isobars close together=strong wind, isobars far apart=light wind (see Lab 2)
• Ridge: a high pressure center
• Synoptic Scale: large weather patterns, say over a 600 to 1000 mile diameter area
• Trade Winds: common northeast winds
• Trough: a low pressure center
• Wind Direction: winds are named after the direction they come from, so easterly winds come from the east, north winds come from the north, sea breezes come from the sea, land breezes come from the land, and so on.

STEP 1: Summarize basic weather patterns

For this assignment, you will need the Flash 6 plug-in for your browser. You probably already have it installed, but if the animations don't work in the exercises below, click the icon to the right and follow instructions to install the plug-in.

Wind and weather patterns are related to the movement and strength of pressure systems. In Hawaii, we are affected by stationary and migratory High pressure centers, migratory Lows in the midlatitudes, and isolated Lows which do not form fronts. In the models below, the circles represent lines of equal pressure (isobars) and the arrows represent wind directions. Remember, near Hawaii, wind flows around High pressure centers in a clockwise direction and around Low pressure centers in a counterclockwise direction. Click each of the three weather pattern images below for an explanation.

High Pressure Centers Stationary and Migratory	Low Pressure Centers Migratory Midlatitude	Low Pressure Centers without Fronts

The writeup for Step 1 should contain:

• Summary of each weather pattern, including a) overview of the relationship between pressure systems and winds over the islands for different configurations, b) weather for each pattern, and c) answers to all of the questions asked in the exercises sections. This part does not need to be long, but should contain enough information to show that you have read all of the material, understand all of the configurations, and practiced all of the exercises.
• NOTE: Do not copy any sentences directly from these lessons. All writing must be in YOUR OWN WORDS.

STEP 2: Record the synoptic forecast for Hawaii for four days

The synoptic forecast simply refers to conditions over a large area, perhaps 1000 miles in diameter. This is a large enough area to include whole pressure systems. The synoptic conditions determine the general weather for the entire Island chain. You will find the synoptic forecast at the National Weather Service site (under the Forecasts menu, click Hawaii -> State Forecast Discussion). Read the forecast each day for four days and include the following in your writeup:

• Time and Date (Important! If you do not give the time and date, I will not accept your lab)
• Brief summary IN YOUR OWN WORDS of the synoptic forecast
• Say which weather pattern you believe exists over Hawaii based on the explanations given in STEP 1.
• Check the satellite image at the National Weather Service site under Current Conditions -> Satellite, then scroll down and click Visible Image under Hourly imagery for the Central Pacific. Do the clouds show evidence of the weather pattern? In what way?

STEP 3: Record the weather at your location

The synoptic forecast refers to a huge area around Hawaii. It controls the general weather, but local conditions can vary a lot. Each time you record the synoptic forecast, step outside and record the following:

• Time and date
• Your location
• General description (fair and sunny, overcast and cold, windy and rainy, or your own description)
• Rain conditions (heavy, light, intermittent, none)
• Cloud type (overcast=stratus, individual=cumulus, high clouds=cirrus)
• Sky cover (what percentage of the sky do you feel is covered by clouds?)
• Temperature (use IR thermometer on shaded side of a tree truck as in previous labs)
• Wind direction (the direction the wind comes from)
• Wind speed estimate (Winds under 3 miles per hour can barely be felt, although smoke will drift. A 3- to 5-mile-per-hour wind can barely be felt on the face. With a 5- to 8-mile-per-hour wind, the leaves in the trees are in constant motion, and with a 12- to 15-mile-per-hour wind, small trees begin to sway.)

Step 4: Conclusions

Give your own thoughts on the topics presented. What did you learn? What questions do you have that were not answered? What was difficult to understand? Feel free to discuss your own experience with Hawaii weather or material that might be included in the future. Also, please tell me about how long it took you to complete this lab and what significant problems you had. Thanks.