(ET) Streamline Configurations
H
H
C
Monsoon
Trough
C
Confluent
Westerlies
Tradewind
Trough
H
H
H
(ET) Streamline Configurations
H
H
C
Monsoon
Trough
C
Confluent
Westerlies
Tradewind
Trough
H
H
H
Diurnal Effects
 Temperature
Range
 Clouds
 Rainfall
3
Diurnal Effects
 Temperature
–
–
–
Range
On small islands and coastlines 3-5°C
with prevailing onshore flow.
On inland locations or coasts 5-10°C
with prevailing land breeze.
In the interior in the dry season >
10°C.
4
Diurnal Effects
 Clouds
– Oceans
Maximum
(0400-0700L),
minimum (1400L-1900L)
– Land
Daytime
maximum,
nocturnal minimum
5
Diurnal Effects
 Rainfall
Nocturnal max over oceans, and
small islands.
– Shower maximum over land in
afternoon.
– Monsoon areas and areas in
disturbances have night to early
morning maximum.
–
6
Tertiary Circulations

Land and sea breezes
–
Sea-breeze characteristics.
Sets up a few hours after sunrise.
 Moves inland until late afternoon to evening.
 Strong breezes may extend 30 - 50 miles inland.

–
Land-breeze characteristics.
Generally shallower with weaker winds than sea breeze.
 Normally does not penetrate as far offshore as sea breeze
penetrates onshore.
 Land breeze front often triggers convection, especially
converging land breezes

7
Rainfall - Special Cases
Prevailing flow onshore:
Prevailing flow offshore
Daytime max on inland
slopes
Afternoon max on
coastline
Day
Sea Breeze
Nighttime max on coastline
Night
Land Breeze
8
Sea Breeze
9
Sea Breeze
10
Land Breeze
11
Tertiary Circulations

Orographically-induced winds.
–
Valley breeze.
 Slopes
warm during day.
 Upslope wind.
 Clouds and convection over peaks during daytime.
–
Mountain breeze.
 Slopes
cool at night.
 Downslope wind.
 Clouds and convection in valleys at night.
12
Tertiary Circulations

Orographically-induced winds.
–
Mountain gap winds.
 Funneling
through passes when surface gradient
across mountains is strong.
 Example: Tehuantepecer winds off Mexico.
13
Tehuantepecers
14
Tehuantepecers
15
Tehuantepecers
16
Upper-Tropospheric Features
 Tropical
Upper-Tropospheric Trough
(TUTT)

Forms in summer hemisphere over mid-oceans.
Subtropical ridge - part that moves
poleward over land masses (North America,
eastern Asia).
Subequatorial ridge - part that stays near
equator over the ET.
17
Upper-Tropospheric Features
 Tropical
Upper-Tropospheric Trough
(TUTT) - Continued Level:
Most intense - 200 mb.
Orientation:
ENE-WSW
Season:
Late April - Mid November (most
intense in August
18
Upper-Tropospheric Features
 Tropical
Upper-Tropospheric Trough
(TUTT) - Continued Position:
South of Surface Subtropical
Ridge over trade winds (convergent
weather associated with TUTT occurs in
tradewinds)
Major Convergent Weather: Few degrees
southeast of upper level center
Weather in axis or Cyclonic Cell Center:
Few clouds, general sinking motion
19
Upper-Tropospheric Features
 Tropical
Upper-Tropospheric Trough
(TUTT) - Continued Temperature:
Cold trough (3-5 degrees
colder than environment, Isold TCU and
TSTMs in TUTT, and center of cells
Axis Windshift: Often an abrupt 180 degree
turn at trough axis
Cirrus Tracers: Indicates > 50 kts either
side of TUTT or embedded cell.
20
21
Overview
 Upper-Tropospheric cyclones (cold lows).
•Strongest 200 to 300 mb and weaken downward.
•TUTT cells are most common examples.
•Center
•Usually clear due to subsidence, though deep cold
cells can have some core convection.
•Periphery
•Upper-level divergence, mostly SE side.
•Satellite Imagery
•Ring of clouds about 140 nm from center.
•Dark round area on water vapor image (best seen in
water vapor!).
22
23
24
TUTT Cell
25
TUTT cell
<------TUTT cell
26
TUTT Cell------>
27
TUTT Cell------>
28
TUTT Cell ---------->
29
TUTT Cell ----------->
in Multispectral Imagery
30
NOGAPS 200 mb
temperatures
<-----Trough
31
Non-severe Weather Systems
and Tertiary Circulations
•Lines
•Tropical Waves
•Vortices
•Land and Sea Breezes
•Valley and Mountain Breezes
32
Non-severe Lines
 Lines
- synoptic scale convergence with
length much greater than width.
– Squall lines
– Cold fronts
– Shear lines
– Surge Lines
– Near Equatorial Convergence Zones
33
Shear Line
34
35
Non-Severe Tropical Waves
National Hurricane Center (NHC)
definition - a trough or cyclonic curvature
maximum in the trade-wind easterlies.
 Sometimes called “Tropical Easterly
Waves” in the Atlantic.
 Originally, this term was based on older
research on the tropics that was based on
sparse surface and upper air data.

36
Non-Severe Tropical Waves
When NHC started using METSAT
imagery in 1967, they saw new aspects of
the so-called “wave” that didn’t fit the
theoretical model.
 Not as common as previously thought;
many systems called waves were actually
vortices
 This model is falling out of favor with
many in the tropical community.

37
The
“Tropical Easterly Wave”
38
Non-Severe Tropical Waves

Characteristics
–
–
Many stem from upper-level cyclones (cold
lows).
Characteristics of Atlantic (easterly) waves.
 Form
over Ethiopian Highlands June to October.
 Move across baroclinic zone south of Sahara often form squall lines.
 Dampen under STR axis in eastern Atlantic and
strengthen near Lesser Antilles.
39
Inverted “Vee” or Screaming Eagle - really a circulation
40
Screaming Eagle
41
Non-Severe Vortices

Fair weather vortices - (Equatorial
anticyclone, heat low, and TUTT)…

Bad weather vortices - (Tropical cyclones,
monsoon depression, west African cyclones,
and mid Tropospheric cyclones).
42
Fair Weather Vortices

Equatorial anticyclones
–
–
–
Found where monsoon trough is more than
10° from equator
Surge from opposite hemisphere crosses
equator and turns anticyclonically
Curved band of cloud seen at leading edge
of anticyclone
43
Fair Weather Vortices

Heat lows/ heat troughs
–
–
–
Low-level air rises over hot land with
subsidence aloft.
Lowest pressure coincides with highest
temperature.
Examples
 Sahara and SW Asia in summer (may be part of
monsoon trough).
 Southern South America, southern and eastern
Africa all year.
44
Bad Weather Vortices

Mid-tropospheric cyclones.
–
Subtropical cyclones.
 Cut-off
portion of deep mid-latitude trough in
the tropics in winter.
 Example: "Kona" storms in Hawaii, cause SW
winds and heavy rains.
–
Arabian Sea cyclones
 Major
rainmaker on west coast of India in SW
monsoon.
 Cloud pattern resembles a typhoon.
45
The Central American Monsoons

Regional Effects

Region normally dominated by NE trade winds.
– Channeling causes 3 quasi stationary cyclones
on Pacific side of Central America which anchor
monsoon trough.
– Northern Hemisphere easterlies to north and
Southern Hemisphere westerlies to south
maintain cyclones.
46
The Central American Monsoons

Panama Bay cyclone
Strongest
–
–
–
anchoring cyclone of the three.
Reinforced by warm ocean currents.
Southwesterly flow channeled cyclonically by
Andes year-round.
Persistent feature May through January.
47
The Central American Monsoons

Lake Nicaragua cyclone
 Anchored
between Nicaragua and Costa Rica.
 Weaker than Panama bay cyclone, persists May November.

Gulf of Tehuantepec (Guatemalan) cyclone.
 Weakest
of the three.
 Maximum strength in October
 Merges with NECZ to west, which is anchored over
SST thermal maximum.
48
The Central American Monsoons

American Monsoons don't meet Ramage's
Criteria because

Semi-annually reversing North-South pressure gradients do
not form.
–
Instead, Central America has a "transitional"
monsoon.
 Oscillates
north - south semiannually.
 Location determined by strengths of NE trades and
Southern Hemisphere southwesterlies.
49
The Central American Monsoons

Monsoon Surges
–
Often caused by low-latitude (10 - 20°N)
tropical cyclones.
 Acceleration
of southwesterlies from south of
monsoon trough.
 NE
flow aloft back into Southern Hemisphere.
50
The Central American Monsoons

Monsoon Surges (Con’t)
Atemporalado
Index
–
“Atemporalado”: term used to describe a winter
rain event in Central America due to a vogorous
cold front or shear line that crosses far enough
south.
–
Often results in Tehuanapecers.
51
The Central American Monsoons
Monsoon Surges (Con’t)
 Rule of Thumb:

Take
SLP difference (DP) between Merida
Mexico and Houston TX.
•
•
•
•
If DP < 12 MB, no SURGE
If DP 12-14 MB, marginal SURGE
If DP 15-19 MB, Nominal SURGE
If DP >20 MB, STRONG SURGE
52
Surge
53
Severe Weather In The Tropics
•Severe Thunderstorms
•Non-Convective Winds
54
Thunderstorms
 More
common in tropics than in high
latitudes
 82 % of thunderstorms are over South
America, Africa, and Indonesia
 18% of thunderstorms are over water
 Most are not severe by mid-latitude
(midwest) standards
55
Severe Thunderstorms

Hail
–

Tornadoes and waterspouts
–

Rare in tropics
The typical WBZ in tropics above 12,000 ft
and is usually over 15,000 ft
Most common in the U.S. and Australia.
Location
–
Most severe storms occur when continental
polar air penetrates the tropics and squall lines
or shear lines develop
56
Severe Thunderstorms
57
58
59
60
61
Bad Weather Vortices

Monsoon depressions
–

Hybrid mid-latitude/tropical cyclone over Bay of
Bengal in summer.
West African cyclones.
–
–
–
Mid-level cyclones that form south of heat trough
in western Africa.
Causes dense stratiform clouds near coast,
convective clouds and squall lines north.
Move west and weaken over Atlantic.
62
Monsoon Depression
63
Monsoon Depression
64
Monsoon Depression
65
Monsoon Depression
66
Monsoon Depression
67
68
69
70
71