The Hurricane Game
For fun (and to learn more Java) I plan to write a program (the “Hurricane Game”) to model inter-seasonal variation in Atlantic storm count. This will be a first-order approximation and will in no way pretend to catch the nuances of a real season. However, I do hope that, despite the crude simplifications, the model will generate realistic inter-seasonal variability. We’ll see!
Below is a general outline and statements of the rules that will govern the program. First, to help explain things, I offer a map (double-click to expand it):
The game begins at the starting line, with a seedling. A seedling moves across the map one square at a time. The seedling starts with an arbitrary initial “score” (a number from 1 to 19) and has the opportunity to pick up additional points as it crosses the map. If it can raise its score to 20 before hitting land then it becomes a named storm!Â
As mentioned, a seedling moves one square at a time. For simplicity in this exercise, the seedling moves due west (left). The latitude at which a seedling launches varies randomly along the heavy black line. (Later, I’ll add a feature to allow seedlings to gain latitude as they progress across the Atlantic.)
A new seedling is launched from the starting line with every eighth move. This way there are usually multiple seedlings on the map. (Why every eighth move? Well, in this model a “move” corresponds to about 12 hours, so a decent seedling is launched from Africa every four days, which is about right.)
Now, how can a seedling earn points so as to be crowned as a named storm? Well, some of the squares on the map award points to a seedling, which the seedling accumulates. To help the explanation, here’s a second map (double-click to expand):
The map contains “green blobs”. Green blobs award points: one point for landing on a light green square, two points for a dark green square. As a seedling moves through a blob it likely lands on green squares and is awarded points, with the aim of accumulating 20 points.
An additional wrinkle: the green blobs are not stationary but instead they move within the red boxes. For every move of the seedlings, the blobs also move. A blob can move one up, one down, one left or one right, at random. It always retains its odd shape, though and stays within its red box.
There are 360 turns in a game (which more-or-less corresponds to the number of 12-hour periods in a hurricane season). Those 360 turns create a total of  45 or so seedlings ( one every eighth turn).
The above approximates the likelihood of a seedling becoming a named storm at a given time in the season, but doesn’t reflect how conditions change during a season, or among seasons. To accomplish that I’ll introduce a few more rules:
* the initial score assigned to a new seedling is 5 during the first 90 turns, which increases to 9 during the next next 90 turns, then increases to 12 during the next 90 turns, then decreases to 9 during the final 90 turns.
* Blob #1 starts with the point totals (1 point for light green, 2 for dark green) shown above for the first 90 turns, then the point totals grow (1.5 light green, 3 dark green) for the next 180 days, then the point totals decrease (0.5 light green, 1 dark green) for the final 90 turns.
* Blob #2 starts with point totals shown (1 light green, 2 dark green) for the first 180 turns, then increase (1.5 light green, 3 dark green) for the final 180 turns.
* If a seedling reaches 20 points and thus becomes a named storm, it “poisons” all the green boxes in a blob square while it travels through that box. The poison is that any green blob square assumes a point value of -1, which is deducted from any other seedling’s score which lands in that square.
How does all of this relate to reality? Well, seedlings are produced at roughly equal frequencies ( every three or four days) and are stronger during midseason than at the beginning or end. The seedlings travel through regions of favorable conditions and regions of neutral (or unfavorable) conditions. Those regions move over time. Those regions strengthen towards midseason and then weaken late in the season. The timing of strengthening and weakening varies by region location.
Later I’ll introduce “red blobs” (regions of unfavorable conditions which subtract points from the seedlings if encountered) and allow seedlings to change latitude as they cross the ocean. I’ll also make the rules governing the strength of seedlings and blobs more spohisticated.
 And, I may create an AMO effect which strengthens the green blobs midway through a 100-year run.
My plan is to make 100-year runs using certain assumptions and rules and see how storm count distribution appears. I’ll then vary the assumptions and see how that impacts things.
Storm count will be a function of defined variables (seedling number, seedling strengths, intensification rules) and of random events (latitude of seedling launches, exact locations of encounters with green intensification squares, proximity to named storms). It’ll be interesting to see the shapes of the 100-year storm distributions, especially as rules are changed.
As always, comments are welcome.