west pacific Typhoon Faxai

[Somerset Squall]

The third tropical depression of the West Pacific season has formed about 300 nautical miles south-southeast of Guam. Winds are at 30kts according to both JMA and JTWC. 03W has increasingly persistant convection over the LLCC, something the system has struggled with over the last day or so. Shear is moderate, but poleward outflow is excellent, which is helping sustain the convection. Shear should ease over the next day or so, promoting strengthening. JTWC expect a peak of 55kts before 03W moves over cooler waters and higher shear again, and begins extratropical transition, expected to begin in 5 days time. 03W is currently in a weakly defined steering envrionment, but ridging to the northeast should excert more dominance over 03W over the next few days, driving the depression to the north.

Edited February 28, 2014 by Somerset Squall

[Somerset Squall]

03W has strengthened and become Tropical Storm Faxai, with winds of 35kts. The storm is still under moderate shear, and the convection is being sheared northwards, leaving the LLCC partially exposed this evening. JTWC still expect strengthening as shear is set to ease, and forecast Faxai to become a minimal typhoon in a few days.

 

 

 

Edited February 28, 2014 by Somerset Squall

[Vorticity0123]

Current state of Faxai

 

The storm is still under moderate shear, and the convection is being sheared northwards, leaving the LLCC partially exposed this evening. 

 

 

Latest satellite imagery from Somerset Squall's post above still shows Faxai is still struggling with this southeasterly shear, with the LLCC on the southern edge of the distorted convective mass. The last few frames of the rainbow-enhanced satellite loop below does show, though, that the convection is slowly edging southward as well. This could indicate that the shear is slowly relaxing, and this might cause strengthening to begin. Moreover, the convection is showing signs of becoming better organized, with some banding features becoming visible in the northwestern sector of this convection. (this is pretty far from the LLCC, though).

 

 

Wind shear analysis from CIMSS shows southeasterly shear over Faxai, which results in the convection being sheared northwestward, as can be seen above. The CIMSS wind shear analysis map can be seen below:

 

The yellow contours indicate shear isolines (lines of equal shear values). The arrows indicate the direction of the wind at high altitude (I think it was 200 hPa, but I am not entirely sure about that)

 

The shear tendency analysis map from CIMSS (see below) shows that the shear has been decreasing over the last 24 hours. This was also visible with the southern-dipping deep convection as stated above.

 

 

The colors show the current strength of the shear. Red colors mean high levels of wind shear, while blue colors indicate very low values of wind shear. The blue broken lines/white lines indicate the shear tendency over the past 24 hours (the change in vertical wind shear over the past 24 hours).

 

Forecasts 

 

The GFS forecasts the system to strengthen to attain a minimum pressure of about 980 hPa. This can be seen below:

 

The mimimum pressure is indicated by the green dot present in the phase diagram (see legend).

 

The track forecast by the GFS shows Faxai will begin a northward motion soon, after the quasi-stationary motion during the past few days. Thereafter, the system is forecast to recurve to the northeast to undergo extratropical transition (this can be seen in the phase diagram. When the system becomes a cold-core low, it is officially an extratropical cyclone).

 

The JTWC forecast generally agrees with the GFS forecast, though the JTWC indicates a more northwestward motion in the mid-term. The forecast can be seen below:

The intensity forecast by the JTWC shows a peak intensity of about 60 knots, which is slightly lower than indicated in previous forecasts.

 

El Niño

 

Jeff Masters (a meteorologist at Wunderground) had a post about the influence of Faxai and Cofie (a tropical cyclone currently active in the southern Pacific) on a possible El Niño event:

 

 

 

 

Two Pacific tropical storms form, boosting the odds of an El Niño
The atmospheric and oceanic conditions in the Equatorial Pacific are ripe for an El Niño event to develop this spring or summer. As detailed in a guest blog post by WSI's Dr. Michael Ventrice on February 21, all that is needed to trigger an El Niño this spring or summer are strong and persistent bursts of westerly winds in the Equatorial Pacific to help push warm water from the Western Pacific Warm Pool eastwards towards South America. Two tropical storms capable of doing just that formed in the Pacific on Friday, boosting the odds that we will see an El Niño event this spring or summer. In the Western Pacific, Tropical Storm Faxai formed Friday morning about 400 miles southeast of Guam. The minimal 40 mph tropical storm is located close to the Equator, at 9°N latitude, which means the the counterclockwise wind circulation around the storm will drive west-to-east winds along the Equator, giving a substantial push to warm waters attempting to slosh eastwards towards South America and start an El Niño event. Faxai is expected to intensify to a Category 1 typhoon by Monday, but is not a threat to any islands. In the South Pacific, Tropical Cyclone Sixteenformed Friday morning near the island of Fiji. This minimal 40 mph tropical storm is moving south-southeast at 10 mph, and is expected to slowly intensify to a strong tropical storm with 70 mph winds by Monday. The clockwise circulation of winds around the storm will also help drive westerly winds near the Equator that will boost the odds of an El Niño event. However, since this storm is farther from the Equator (16°S), it will not have a strong an impact on boosting El Niño odds as Tropical Storm Faxai will.

 

The full blog post can be found below:

 

http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2639

 

Sources:

http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=westpac&sat=wgms∏=wvir&zoom=&time

http://www.ssd.noaa.gov/PS/TROP/floaters/03W/03W_floater.html

http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/14030106/4.html

http://www.usno.navy.mil/JTWC/

http://dutch.wunderground.com/blog/JeffMasters/comment.html?entrynum=2639 

Edited March 1, 2014 by Vorticity0123

[Somerset Squall]

Faxai has been moving erratically over the last 24hrs, completing a loop. The storm strengthened to 50kts earlier, but has since weakened to 45kts due to an increase in shear. This shear is not expected to last, and Faxai should resume strengthening soon as it moves northwards as the ridge to the east gains steering influence.

[Somerset Squall]

Faxai is strengthening as it moves north, east of Guam. Winds are up to 55kts. Faxai has developed a central dense overcast, an indicator that shear has lessened. Further strengthening is likely over the next 24hrs, and Faxai will likely become the season's first typhoon strength system if current trends continue.

[Vorticity0123]

Faxai is strengthening as it moves north, east of Guam. Winds are up to 55kts. Faxai has developed a central dense overcast, an indicator that shear has lessened. Further strengthening is likely over the next 24hrs, and Faxai will likely become the season's first typhoon strength system if current trends continue.

 

And this is exactly what has happened! Faxai has produced a burst of rapid intensification, which has led the JTWC to amend their advisory they issued. From the Prognostic Reasoning (by JTWC):

 

 

 

JUSTIFICATION FOR AMENDMENT: CHANGED THE INTENSITY FORECAST DUE TO RE-EVALUATION OF THE CURRENT INTENSITY. 

 

In the Dvorak loop below, the development of a warm spot (equivalent to eye feature) can be seen developing, and transforming into a tiny eye. This eye is encircled by very intense convection (the grey shadings on the white in the image below):

 

 

Of note is that two distinct phases can be detected in the eye formation. In the first set of images, a circular banding type eye is visible. However, on the last few frames, the convection seems to be becoming more ragged, giving the impression of a more disorganized cyclone.

 

The intensity assessed by JTWC is 65 knots, which makes Faxai the first typhoon of the 2014 Pacific typhoon season. Of note is that this intensity estimate does seem a little bit on the conservative side to me, based on the eye feature. Latest satellite intensity estimates from CIMSS have been 85, 88 and 89 kt from ADT, AMSU and SATCON, respectively, which argues for a stronger cyclone than the JTWC is currently indicating.

 

The satellite intensity estimates curve from ADT can be seen below:

 

What can be seen is that Faxai strengthened from 50 to about 80 kt in just 24 hours! (compare the intensity estimates at 12 UTC 03-03-2014 and 12 UTC 04-03-2014, respectively)

 

Future of Faxai

 

Despite the rapid intensification phase we are currently observing, the life of Faxai as a tropical cyclone will be about to end. For the reasoning, check the map below:

 

C is the current position of Faxai, and the sea surface temperatures are indicated by the colours.

 

What can be seen is about to cross the 26*C isotherm. This means that the cyclone is almost over waters which are too cool to sustain a tropical cyclone. As a result, weakening will be imminent in the short term. Moreover, Faxai will soon be undergoing extratropical transition while recurving toward the northeast and east, as is indicated by the JTWC: 

 

 

 

TY 03W IS EXPECTED TO RECURVE AROUND THE WESTERN PERIPHERY OF

THE STR AS IT ACCELERATES NORTHEASTWARD INTO THE MIDLATITUDE

WESTERLIES. INCREASING VWS FROM THE WESTERLIES AND DECREASING SEA

SURFACE TEMPERATURES WILL GRADUALLY ERODE THE SYSTEM AND WILL LEAD

TO EXTRA-TROPICAL TRANSITION (ETT) BY TAU 36.

 

Sources:

http://www.usno.navy.mil/JTWC/

http://www.ssd.noaa.gov/PS/TROP/floaters/

http://tropic.ssec.wisc.edu/#

http://moe.met.fsu.edu/cyclonephase/gfs/fcst/archive/14030412/2.html

Edited March 4, 2014 by Vorticity0123

[Somerset Squall]

Winds have been upped to 75kts by JTWC, they expect a peak of 80kts in 12hrs, followed by weakening and extratropical transition for reasons explained by Vorticity above.

An impressive early season West Pacific system!

Edited March 4, 2014 by Somerset Squall

[Somerset Squall]

What a difference 24hrs makes! JTWC have issued the last advisory as all convection associated with Faxai has vanished at an alarming rate, and the remnant low has become extratropical.