What happens if a weather system (such as a depression or hurricane) crosses
the equator?

Does it stop and start spinning in the other direction?

Brendan

"Brendan DJ Murphy" wrote in message
...
What happens if a weather system (such as a depression or hurricane) crosses
the equator?

Does it stop and start spinning in the other direction?

The simple answer to this is that it doesn't or rather *can't*.

Frontal depressions don't form anywhere near the equator anyway
and even hurricanes can't form any nearer than about 5 degrees
from it. It's all to do with the Coriolis force. A hurricane could never
cross the equator as it is always being forced away from it.

Col
--
Bolton, Lancashire.
160m asl.
http://www.reddwarfer.btinternet.co.uk
http://www.reddwarfer.btinternet.co....rPictures.html

Col wrote in message ...

"Brendan DJ Murphy" wrote in message
...
What happens if a weather system (such as a depression or hurricane) crosses
the equator?

Does it stop and start spinning in the other direction?

The simple answer to this is that it doesn't or rather *can't*.

Frontal depressions don't form anywhere near the equator anyway
and even hurricanes can't form any nearer than about 5 degrees
from it. It's all to do with the Coriolis force. A hurricane could never
cross the equator as it is always being forced away from it.

Col
--

OTOH I have seen satellite movie loops clearly showing high cloud crossing the
equator from one system to another.

If you ignore meteological "objects" like hurricanes and depressions there is
nothing to stop cloud and moisture from crossing the equator. Winds do blow
across the equator driven by thermal imbalances, just as winds blow straight
over the poles as well.

Will.
--
" A cup is most useful when empty "
-------------------------------------------------------------------------------
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"Brendan DJ Murphy" wrote in message
...
What happens if a weather system (such as a depression or
hurricane) crosses the equator?

Does it stop and start spinning in the other direction?

Brendan, a typhoon got extremely close to the equator in
December 2001, breaking all the rules. I haven't read
anything about it since, but it would be very surprised
and disappointed if it hadn't been examined in great
detail in some publication or other ... anyone know?

As an academic exercise, try drawing the streamlines
in a barometric depression as it crosses the equator.

Here is what the Joint Typhoon Warning Center put
out:


WDPN31 PGTW 271500
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM

32W (VAMEI) WARNING NR03//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 271200Z2 TO 301200Z6 DEC 01.
A. TROPICAL STORM (TS) 32W (VANMEI) MOVED OVER

THE SOUTHEASTERN COAST OF MALAYSIA, ABOUT 30 NM

NORTHEAST OF SINGAPORE, ATAPPROXIMATELY 270830Z0.

THE SYSTEM WAS CLASSIFIED AS A TYPHOON AS IT
MOVED ONSHORE PACKING SUSTAINED WINDS OF 75 KNOTS

WITH GUSTS TO 90 KNOTS. TS 32W, LOCATED APPROXIMATELY

20 NM NORTH OF SINGAPORE, WAS MOVING WESTWARD AT

05 KNOTS DURING THE PAST 6 HOURS. THE WARNING
POSITION WAS BASED ON 271130Z4 ENHANCED INFRARED

IMAGERY AND SYNOPTIC DATA. THE WARNING INTENSITY IS

BASED SATELLITE INTENSITY ESTIMATES OF 40 TO 55 KNOTS.

THE SYSTEM APPEARS TO BE WEAKENING AS RAPIDLY AS IT

DEVELOPED. INFRARED ANIMATION DEPICTS A SYSTEM
SHRINKING IN COVERAGE WHILE THE LATEST (271104Z5) SSM/I

PASS FAILED TO REVEAL A DISTINCT LLCC. REMAINING DEEP

CONVECTION IS CONFINED TO THE SOUTHERN TIP OF MALAYSIA

AND THE ENTRANCE TO THE STRAIT OF MALACCA.


B. IT SEEMS THAT THIS SYSTEM HAS BROKEN ALL THE

PHYSICAL RULES IN RELATION TO GENESIS ORIGIN. A VERY

SMALL CORIOLIS PARAMETER, IF ANY, AND LARGE PRESSURE

GRADIENTS, ALL SUPPORTING THE IMPOSSIBILITY OF A TYPHOON

STRENGTH SYSTEM IN SUCH A CLOSE PROXIMITY TO THE EQUATOR.

I WOULD GATHER A GUESS THAT THE WINDS WITHIN THE SMALL,

INTENSE, EYEWALL WERE POSSIBLY CYCLOSTROPHIC IN NATURE.

A MID-LEVEL RIDGE IS FORECAST TO REMAIN OVER SOUTHEAST

ASIA THROUGH THE FORECAST PERIOD. THEREFORE, TS 32W

SHOULD TRACK IN A WEST-NORTHWESTWARD. THE AVAILABLE

DYNAMICAL MODELS THAT REFLECT THE SMALL SYSTEM,

(NOGAPS, THE AVN RUN, GFDN, AND THE JMA GLOBAL) AGREE

WITH THE ABOVE SYNOPTIC SCENARIO. THEREFORE, OUR FORECAST

IS BASED ON PERSISTENCE AND A BLEND OF THE AVAILABLE MODELS.


C. THE SYSTEM IS EXPECTED TO CONTINUE ON A WEAKENING

TREND AS IT TRACKS OVER THE PENINSULA AND SUMATRA.

AFTERWARD, RE-INTENSIFICATION IS POSSIBLE ONLY IF THE

LOW-LEVEL CIRCULATION SURVIVES THE TRACK OVER SUMATRA

AND INTO THE BAY OF BENGAL.



D. WIND RADII ANALYSIS ARE BASED ON SYNOPTIC DATA

AND MICROWAVEIMAGERY.


FORECAST TEAM: ROBERTS/HARRISON/BOSTIC/EDBERG//



Philip Eden