BROADSCALE ENVIRONMENT - LARGE SCALE CONDITIONS

•Tropical waves (MJO, ER waves)

•Monsoon or trade wind surges

•Upper trough within 25 deg to the west or retrogressing upper low

•Broad scale outflow channels – fanning of cirrus

BROADSCALE ENVIRONMENT  -  NEAR SUSPECT AREA

•low to mid level trough

•light upper winds

•weak shear in area, stronger shear further away

•deep moist air in all sectors

DEVELOPMENT OF EXISTING DISTURBANCE - CIRCULATION

•identifiable cyclonic circulations (low/mid level circulation centre = cloud lines)

•vertically stacked circulation (surface – 500 hPa)

•significant (vertically stacked & round) mid level circulation (850-500 hPa ,15-25 kt)

DEVELOPMENT OF EXISTING DISTURBANCE - DEEP CONVECTION

•deep convection (cold cloud tops <-65C) < 2 degree radius, persisting 6-12 hrs.

•Pressure falls > 2 hPa within 3 degree of centre

A.Is the MJO active in our longitudes ?
MJO OLR anomalies | Real time Multivariate MJO Index

B.Are there any tropical/easterly waves currently propagating towards the suspect area?
All Mode OLR anomalies | Tropical Wave Forecast

C.Are there any strong low-level monsoon or trade flows feeding into the suspect area now? (Not necessarily a surge but a maintenance of strong flow).
CIMMS | Quickscat | TXLAPS 850hPa

D.Is there a low/mid level trough in the suspect area now?
CIMMS | Gradient 00Z | Gradient 12Z | TXLAPS 900hPa | TXLAPS 850hPa

E.Are the winds at 200/250 hPa over the suspect area < 20 knots?
CIMMS | 200 hPa 00Z | 200 hPa 12Z | TXLAPS 200hPa

F.Is there low (5-15 kt) 850-200 hPa vertical shear near the area and stronger (>15 kt) shear away (5-10°) from the suspect area?
CIMSS | TXLAPS 850-200hPa shear

G.Is there a synoptic feature creating strong upper divergence above the suspect area? For example an upper trough or retrogressing upper low within 25 degrees to the west, or a strong equatorial jet with the ridge centre over the area.
CIMSS | TXLAPS 200hPa Div

H.Is there evidence on satellite imagery or upper streamline charts of at least one outflow channel?
GOES-9 | 200 hPa 00Z | 200 hPa 12Z

I.Is there evidence of two outflow channels or fanning of cirrus (equatorward and eastward of CDO)? If so consider rapid development potential.
GOES-9

J.Is the suspect area being fed by deep moist air in all sectors?
SSMI Precip Water | GOES-9 WV | Darwin | Gove | Weipa | Broome | TXLAPS 850hPa RH | TXLAPS 700hPa RH | TXLAPS 500hPa RH

Vortical towers

Cores of deep Cb convection forming in a vorticity rich pre-hurricane environment.

The towers contain a lot of vorticity, they are inertially stable.

So latent heat generated becomes trapped in the rotating convective cores.

Their lifetime is of the order of one hour.

First Stage – Preconditioning Phase

Vortical hot towers compete for CAPE and angular momentum.

Vorticity generated by the towers (updraft) passes to the environment after the towers decay. 

Environmental vorticity increases.

Second Stage - Multiple Merger and Axisymmetrization Phase

Hot towers coalesce in an environment of enhanced vorticity (diabatic mergers).

This coalescence quadruples the horizontal scale of relative vorticity.

Tangential winds increase, and warming at low levels.

The TC is born (model data indicates the vortex merger stage lasts from 27-36hrs)

Upon Receipt of Warning:
1. Plot the current and forecast 24 hour storm  positions and forecast radius of 35 kt winds.
2. Using a compass extend the radius of the forecast 24 hour 35 kt wind area by 100 NM.
3. Draw tangents relative to the direction of the storm from the 35 kt radius (current position) to the outermost radius at the 24 hr forecast position.  Avoid the DANGER AREA
4. Use the same procedure for the 48 and 72 hr forecast positions, however, use 200 and 300 NM radii/respectively.
   Avoid the DANGER AREA.



TROPICAL CYCLONE EVASION

- Meteorological elements are not uniformly distributed throughout a tropical
Storm is divided into left/right semicircles and quadrants, relative to the direction of motion
Usually strongest winds are on right side in N.H. (added to motion)

- Ship in the “Dangerous” (right) semi-circle:
1.  Maneuver ship so relative wind is from 045 degrees to starboard.
2.  Continually hold course with respect to relative wind, making best way possible.

- Ship in the “Less Dangerous” (left) semi-circle:
1.  Maneuver ship so that relative wind is from 135 degrees to starboard.
2.  Hold course with respect to relative wind, and make best SOA.

- Never cross the “T”:    Do not plan to cross the track of a hurricane.

NEVER LEFT TO RIGHT!  Respect the negative effects that heavy weather places on vessel speed/handling. Sudden accelerations in hurricane motion can ultimately place a vessel in conditions not originally expected, resulting in disaster! 

Adjustments to course & speed in order to remain clear of the danger area in a hurricane are the most prudent navigation decisions a mariner can make in these instances. 

If it becomes necessary to cross the “T” right to left, ensure you are at least 300NM from the center. 

Follow the 1 – 2 – 3 Rule

- Monitor warnings and advisories to prevent an encounter.

Forecast Track Tendencies:  Comparison of the most recent NHC forecast track with forecast tracks from the past 24 hours can be useful for determining a trend in the forecast motion of a hurricane. 

For instance, a comparison of forecast tracks issued every 6 hours over the last 24 hours, may show a noticeable shift right or left (with respect to storm motion) in the forecast track of a hurricane. This information may provide some indication as to how the forecast & actual hurricane track are trending and provide more guidance in navigation planning for avoidance, particularly in the 2-3 day forecast range & beyond.

Stay Inport or Ride it out at Sea?
Factors to consider!
The decision to leave port for hurricane avoidance must be made very early, and must be balanced with a number of other factors

-  Storm Intensity, Size, Strength, and Speed.  
-  Port Facilities, Berthing & Shelter Requirements 
-  24 hours prior to onset of gale force winds.
-  Probability of Hit (angle of approach)
-  Vessel, size, speed, engineering status
-  Time window to clear last vessel
-  Vessel Route (safe, heavy seas, etc...)


* Early decisions to leave port in an attempt to avoid hurricanes are crucial.*