Tropical Revolving Storms

Question 1

Which way do TRS blow in the northern hemisphere?

Answer 1

Anticlockwise

Question 2

Which way do TRS blow in the southern hemisphere?

Answer 2

Clockwise

Question 3

What is the minimum required sea surface temperature for a TRS to form?

Answer 3

26 degrees Celsius

Question 4

At what time of year are TRS most common?

Answer 4

In late summer and early autumn in the respective hemisphere

Question 5

At what latitudes do TRS usually form during high season in the northern hemisphere?

Answer 5

Between 10-25 degrees North

Question 6

At what latitudes do TRS usually form during early/late season in the northern hemisphere?

Answer 6

Between 5-15 degrees North

Question 7

At what latitudes do TRS usually form in the southern hemisphere?

Answer 7

Between 5-18 degrees South

Question 8

Explain the typical movement of a TRS in the northern hemisphere

Answer 8

It will begin travelling in a WNW direction before recurving at around 25 degrees North. It will be heading NE by 30 degrees North

Question 9

Explain the typical movement of a TRS in the southern hemisphere

Answer 9

It will begin travelling in a WSW direction before recurving at around 15-20 degrees South. It will then travel in a SE direction

Question 10

Name the 5 different corrections to be made to a ship’s barometer

Answer 10

Height
Latitude
Temperature
Index error
Diurnal variation

Question 11

What are the four main precursory indications of a TRS in the vicinity?

Answer 11

1. The corrected barometer reads 3hPa below average for the time of year (as per Sailing Directions) = suspected TRS. 5hPa drop = certain TRS
2. Appreciable change in wind speed and/or direction
3. Long, low swell coming from the direction of the storm’s centre
4. Extensive cirrus clouds, followed by Altostratus and then broken Cumulus as the storm gets closer

Question 12

In the northern hemisphere, what does it mean if you are in the vicinity of a TRS and the wind is veering?

Answer 12

You are in the dangerous semicircle

Question 13

In the northern hemisphere, what does it mean if you are in the vicinity of a TRS and the wind is backing?

Answer 13

You are in the navigable semicircle

Question 14

What does it mean if you are in the vicinity of a TRS and the wind direction is steady?

Answer 14

You are in the path of the TRS

Question 15

In the southern hemisphere, what does it mean if you are in the vicinity of a TRS and the wind is veering?

Answer 15

You are in the navigable semicircle

Question 16

In the southern hemisphere, what does it mean if you are in the vicinity of a TRS and the wind is backing?

Answer 16

You are in the dangerous semicircle

Question 17

In the northern hemisphere, what action should you take if you find yourself in the dangerous semicircle of a TRS?

Answer 17

Speed = full ahead

Put wind on the starboard bow and alter course to starboard as the wind veers

Question 18

In the northern hemisphere, what action should you take if you find yourself in the navigable semicircle of a TRS?

Answer 18

Speed = full ahead

Put wind on the starboard quarter and alter course to port as the wind backs

Question 19

In the southern hemisphere, what action should you take if you find yourself in the dangerous semicircle of a TRS?

Answer 19

Speed = full ahead

Put wind on the port bow and alter course to port as the wind backs

Question 20

In the southern hemisphere, what action should you take if you find yourself in the navigable semicircle of a TRS?

Answer 20

Speed = full ahead

Put wind on the port quarter and alter course to starboard as the wind veers

Question 21

What is the ITCZ, and what other name is it known by?

Answer 21

The Intertropical Convergence Zone, AKA The Doldrums.

It is a band of low pressure around the Earth which typically lies near the equator, although it does move year-round.

Question 22

Explain why storms and heavy rain can be present in the typically-calm ITCZ

Answer 22

The trade winds of the north and south hemispheres converge here, leading to the development of thunderstorms and heavy rain.

Question 23

What are the horse latitudes and what weather conditions can be expected?

Answer 23

Area of high pressure in the sub-tropics (e.g. Azores). Weather is typically benign.

Question 24

What is the Hadley Cell and where is it found?

Answer 24

It is the circulation of air that lies between 10-15 kilometres above the Earth’s surface at mid latitudes (think 0-30 degrees).

It forms as a result of the air in the ITCZ rising above the surface and moving toward the poles before descending in the horse latitudes, then making its way back toward the equator

Question 25

Explain the movement of the ITCZ

Answer 25

The ITCZ moves throughout the year and follows the migration of the sun’s overhead position with a delay of around 1-2 months.

As the ocean heats up more slowly than land, the ITCZ tends to move further north and south over land areas than over water