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Tropical Depression 21W Situation Map

Tropical Cyclone Formation

Tropical Cyclone Genesis is the technical term for the process of storm formation that leads ultimately to what are called hurricanes, typhoons, or tropical cyclones in various parts of the world.

This occurs when, in the Northern Hemisphere, the Intertropical Convergence Zone, or ITCZ, shifts northward out of the doldrums and atmospheric conditions become favorable for tropical cyclone formation after about the middle of May.

A series of low-pressure ripples develops within the ITCZ. These are known as tropical waves and progress from east to west. In the late season, they typically shift their movement toward the west-nothwest, or even northwest, after crossing 45° or 50° W longitude. Full Article

Tropical Depression 21W Forecast Graphic
Tropical Depression 21W Forecast Track (Joint Typhoon Warning Center)
Tropical Depression 21W Storm-Centered Infrared
Tropical Depression 21W Storm-Centered Enhanced Infrared
Tropical Depression 21W Storm-Centered Visible
Tropical Depression 21W Warning Text (JTWC)
WTPN31 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL DEPRESSION 21W (TWENTYONE) WARNING NR 002//
RMKS/
1. TROPICAL DEPRESSION 21W (TWENTYONE) WARNING NR 002    
   01 ACTIVE TROPICAL CYCLONE IN NORTHWESTPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   161800Z --- NEAR 18.1N 129.5E
     MOVEMENT PAST SIX HOURS - 300 DEGREES AT 06 KTS
     POSITION ACCURATE TO WITHIN 040 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   REPEAT POSIT: 18.1N 129.5E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   170600Z --- 18.6N 127.9E
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   VECTOR TO 24 HR POSIT: 280 DEG/ 06 KTS
    ---
   24 HRS, VALID AT:
   171800Z --- 18.8N 126.6E
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   VECTOR TO 36 HR POSIT: 270 DEG/ 07 KTS
    ---
   36 HRS, VALID AT:
   180600Z --- 18.8N 125.2E
   MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   VECTOR TO 48 HR POSIT: 265 DEG/ 06 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   181800Z --- 18.7N 123.9E
   MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   VECTOR TO 72 HR POSIT: 255 DEG/ 04 KTS
    ---
   72 HRS, VALID AT:
   191800Z --- 18.3N 122.2E
   MAX SUSTAINED WINDS - 020 KT, GUSTS 030 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
    ---
REMARKS:
162100Z POSITION NEAR 18.2N 129.1E.
16OCT19. TROPICAL DEPRESSION 21W (TWENTYONE), LOCATED APPROXIMATELY
532 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED
WEST-NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. MAXIMUM
SIGNIFICANT WAVE HEIGHT AT 161800Z IS 8 FEET. NEXT WARNINGS AT
170300Z, 170900Z, 171500Z AND 172100Z.//
NNNN
Tropical Depression 21W Prognostic Reasoning (JTWC)
WDPN31 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE)
WARNING NR 002//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 21W (TWENTYONE), LOCATED APPROXIMATELY
532 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED
WEST-NORTHWESTWARD AT 06 KNOTS (KTS) OVER THE PAST SIX HOURS.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS FLARING
CONVECTION LOCATED OVER A DEVELOPING LOW LEVEL CIRCULATION (LLC). THE
MAJORITY OF THE ASSOCIATED CONVECTION IS LOCATED IN THE NORTHEAST
QUADRANT OF THE SYSTEM WITH SOME CONVECTIVE BANDING, SUPPORTED BY
161838Z SSMI 37GHZ MICROWAVE IMAGE. THE INITIAL POSITION IS PLACED
WITH FAIR CONFIDENCE BASED ON EIR AND THE AFOREMENTIONED MICROWAVE
IMAGE. THE INITIAL INTENSITY IS SET AT 25 KTS BASED ON THE WIND FIELD
OBSERVED IN THE 161204Z ASCAT-C IMAGE AND DVORAK CURRENT INTENSITY
(CI) ESTIMATES OF T1.5/25 KTS FROM PGTW AND RJTD. TD 21W IS
TRANSITING THROUGH AN AREA OF LOW (10-15 KTS) VERTICAL WIND SHEAR
(VWS) WITH GOOD POLEWARD AND EQUATORWARD OUTFLOW. SEA SURFACE
TEMPERATURES (SST) ARE FAVORABLE AT 28-29 CELSIUS. TD 21W IS TRACKING
ALONG THE SOUTHERN PERIPHERY OF THE LOW-LEVEL SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. UNDER THE STEERING INFLUENCE OF THE AFOREMENTIONED STR, TD 21W
WILL TRACK WEST-NORTHWESTWARD THEN WESTWARD THROUGH TAU 36.
AFTERWARDS, INTERACTION WITH A NORTHEAST SURGE EVENT IS EXPECTED TO
TURN THE SYSTEM WEST-SOUTHWESTWARD. UPPER LEVEL DIVERGENCE IS
SLIGHTLY OFFSET TO THE NORTHEAST AND WILL SLOWLY DECREASE OVER THE
NEXT 36-48 HOURS. THUS, TD 21W IS FORECAST TO HAVE A BRIEF PERIOD FOR
INTENSIFICATION TO 30 KNOTS PRIOR TO GRADUALLY DISSIPATING AS IT
INTERACTS WITH THE NORTHEAST SURGE AND TERRAIN ON LUZON. MODEL
GUIDANCE IS LIMITED TO AEMN, ECMWF AND NVGM DUE TO THE WEAK NATURE OF
THIS SYSTEM. MODELS ARE IN GOOD AGREEMENT WITH NVGM AS THE
SOUTHERNMOST OUTLIER, LENDING TO HIGH CONFIDENCE IN THE JTWC FORECAST
TRACK.//
NNNN
Tropical Depression 21W JMV 3.0 Data (JTWC)
WTPN51 PGTW 162100    
WARNING    ATCG MIL 21W NWP 191016205307
2019101618 21W TWENTYONE  002  01 300 06 SATL 040
T000 181N 1295E 025 
T012 186N 1279E 030 
T024 188N 1266E 030 
T036 188N 1252E 025 
T048 187N 1239E 025 
T072 183N 1222E 020 
AMP
    048HR DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
    072HR DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
SUBJ:  TROPICAL DEPRESSION 21W (TWENTYONE) WARNING NR 002    
1. TROPICAL DEPRESSION 21W (TWENTYONE) WARNING NR 002    
   01 ACTIVE TROPICAL CYCLONE IN NORTHWESTPAC
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   161800Z --- NEAR 18.1N 129.5E
     MOVEMENT PAST SIX HOURS - 300 DEGREES AT 06 KTS
     POSITION ACCURATE TO WITHIN 040 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   REPEAT POSIT: 18.1N 129.5E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   170600Z --- 18.6N 127.9E
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   VECTOR TO 24 HR POSIT: 280 DEG/ 06 KTS
    ---
   24 HRS, VALID AT:
   171800Z --- 18.8N 126.6E
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   VECTOR TO 36 HR POSIT: 270 DEG/ 07 KTS
    ---
   36 HRS, VALID AT:
   180600Z --- 18.8N 125.2E
   MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   VECTOR TO 48 HR POSIT: 265 DEG/ 06 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   181800Z --- 18.7N 123.9E
   MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   VECTOR TO 72 HR POSIT: 255 DEG/ 04 KTS
    ---
   72 HRS, VALID AT:
   191800Z --- 18.3N 122.2E
   MAX SUSTAINED WINDS - 020 KT, GUSTS 030 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
    ---
REMARKS:
162100Z POSITION NEAR 18.2N 129.1E.
16OCT19. TROPICAL DEPRESSION 21W (TWENTYONE), LOCATED APPROXIMATELY 532 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 161800Z IS 8 FEET. NEXT WARNINGS AT 170300Z, 170900Z, 171500Z AND 172100Z.//
2119101518 166N1332E  20
2119101600 169N1321E  20
2119101606 175N1310E  20
2119101612 178N1301E  25
2119101618 181N1295E  25
NNNN

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