Friday, June 22, 2012

Isles of the Saharan Sea: The Weather...

Good Afternoon, All:

I just wanted to interrupt the posts on encounters temporarily to talk about the weather. The weather of the Isles of the Saharan Sea typically follows a tropical pattern, with a longer dry season and a shorter wet season roughly a third the length of the dry season. Major monsoons and frequent thunderstorms strike during the wet season, during which only the foolish attempt to sail. Islanders typically mark the passage of long periods of time in "monsoons", referring to the shorter wet season. This roughly corresponds to a year in the Outer World, as the size and intensity of the Eternal Sun cycles on an annual basis.

Islanders typically experience the following weather patterns of note:
  1. Rainfall is quite heavy, particularly during the wet season. Even during the dry season, rain will frequently fall, but not nearly in the quantities experienced in the wet season.
  2. When standing on the coast, breezes typically blow in from the sea during the wet season, and blow out from the land during the dry season.
  3. The higher the elevation, the cooler the temperature and the greater the amount of precipitation.
  4. An average of ten major tropical storms occur every year, and can include hurricanes and monsoons. Hurricanes have an average Travel Speed of 10, and typically lasts for 1d6+1 days.

The weather system described here is based, at least loosely, on the article "Weathering The Storms", which appeared in Dragon Magazine #137. The process is pretty straightforward, and is used to generate weather for a month at a time:
  1. Roll a d20 on on the appropriate Temperature Table to determine the month's usual temperature. If something seems odd, then reroll or create an in-game reason for the result to exist.
  2. Roll a d100 thirty times to determine how many days of rain occur in that month.
  3. Arrange rain days to taste.
  4. For each rain day (or group of rain days), determine the Rain Type. If you are determining this for a group of consecutive days, roll 1d4+2 instead of 1d6.
  5. For each non-rain day, determine the Non-Rain Type.
  6. Roll a d12 to determine Wind Direction as needed.

Table: Dry Season Temperatures
1d20DesertMountainsForest/Marsh/AquaticHills/Plains
1CoolCoolWarmWarm
2-10HotWarmHotHot
11-19HotHotHotVery Hot
20Very HotVery HotVery HotExtremely Hot
Rain5%40%15%10%

Table: Wet Season Temperatures
1d20DesertMountainsForest/Marsh/AquaticHills/Plains
1CoolCoolWarmWarm
2-10WarmCoolHotHot
11-19WarmWarmHotVery Hot
20HotHotVery HotExtremely Hot
Rain5%40%90%85%

Table: Rain Type
1d6Rain TypeWind Speed
1DrizzleLight
2DrizzleLight
3Steady RainModerate
4Steady RainStrong
5StormSevere
6Powerful StormWindstorm (20% chance of Hurricane)

Table: Non-Rain Type
1d6Wind Speed
1Light
2Light
3Light
4Moderate
5Strong
6Severe

Table: Wind Direction
1d12Wind Blows Toward...
1-2North
3-5Northeast
6-7East
8Southeast
9South
10Southwest
11West
12Northwest
As always, the above is subject to change once I implement it in-game. If it doesn't prove to work effectively, I'll just swap it out with some other approach, such as a Random Encounter table littered with weather effects in addition to monsters.

If you have any thoughts or suggestions you would like to make that might enhance this simple weather system, please feel free to share.

Enjoy,
Flynn

2 comments:

John said...

I think your wind structure by season is probably inconsistent with earth's patterns. Generally, winds coming off the ocean are laden with moisture, and are the cause of India's monsoons, New England's Nor'easters, and Seattle's ridiculous drizzle. Winds from landward are usually drier.

Flynn said...

Great point, John! I must have gotten mixed up, or just wasn't paying attention when I was writing that up. I'll change it in the post above. :)

With Regards,
Flynn