Archive for the ‘ Extra Tropical Transiton ’ Category

Jangmi fades after ET

Wednesday, October 1st, 2008

The last warning for Jangmi from JTWC was issued at 21Z on the 30th of September. Jangmi had

max sustained winds at 35 kts with gusts to 45 kts. As it moved into the midlatitude westerlies it completed

extra-tropical transition. Attached is an IR image with overlayed divergence and upper-level AMVs. The animation ends on 13Z on October 1st:

You can see how sheared the system is and that it’s lost any symmetry. According to the GFS phase diagram Jangmi has already fully undergone extra-tropical transition. It still has some anticyclonic outflow to the south, but it is impeded to its north from the midlatitude jet.

Unfortunately, the C-130 has finished flying for the experiment and the P-3 has been down due to an AC problem. But, we will have flight data from the Falcon (and perhaps the DOTSTAR too) which will be vital for AMV validation.

Attached is the planned route for the Falcon at 00Z on the 1st of October, plotted over ECMWF forecast upper-level winds and low-level vorticity:

As you can see they are attempting to sample Jangmi’s outflow and interaction with the midlatitude jet.  The model output shown above agrees fairly well with the 200 hPa streamlines from the AMVs

And what about future development?

The ECMWF does not do much with it in terms of development. The GFS hints at Jangmi merging with another disturbance and developing something downwind. The NOGAPS and Met Office model hint at something as well. These should be well out of range for the research aircraft, but perhaps the data we’ve obtained from the experiments will help downstream forecasts.

Tropical Storm Jangmi 12Z September 29th, 2008

Monday, September 29th, 2008

At 12Z, September 29th JTWC analyzed Jangmi at  27.2N 122.1E, moving 09 kts at 065 degrees with an intensity of 055 kt, and gusts of 070 kts.

Attached is the IR, upper-level AMV, and analyzed divergence animation valid at 14Z:

Jangmi has been hit hard by shear from the upper-level westerlies off of China. These westerlies  have enhanced the outflow and divergence to Jangmi’s northeast, but the associated shear has helped weaken the storm significantly as well.

As of 13Z the ADT analyzed an intensity of 39 kts, and the 08Z AMSU and SATCON had an intensity of 45 kts. The 12Z TMI image shows some convection to the northeast as well, but no organized eyewall.

Looking at the phase diagrams, the GFS diagram shows ET is underway, loosing its symmetric representation already, and then becoming cold-core by the 2nd of October. The Met Office diagram has similar timing. The NOGAPS analysis is similar early on, but then becomes more symmetric before becoming cold core.

The models are moving the system eastward, well south of Japan, and shearing it out quickly. They vary a bit in their frontal development and placement, however. By 00Z on the 3rd, all of the models except the NOGAPS analyze the system around 30N, 140E. The NOGAPS, the most symmetric of the analyzed systems, is also the slowest; bringing it to 30N 130E by that same time. The ECMWF seems the most sheared.

Model forecasts: ECMWF,Met Office,GFS, NOGAPS.

Either way, in the shorter term, this system is likely to weaken in the near time. The recurvature is interesting, because it was only recently predicted by the models. Looking back, the model consensus forecast on the 26th still shows Jangmi heading into China. By the 27th, the 12Z run began forecasting recurvature. This may be a good potential case to look at the effect of observations to see if the track prediction can be improved.

Sinlaku: Forecast and future

Friday, September 19th, 2008

By T+48 (00Z on the 19th) most of the models are fairly similar. All of the models except the EC seem to have maintained symmetry by that time. Almost all of the models have Sinlaku near about 150E, although the Met Office model is a bit slower with its eastward progression. The NOGAPS and the GFS are a bit farther north than the other models as well. After ET sets in, the models move the former Sinlaku at slightly different paces. NOGAPS seems a bit faster by +108, bringing Sinlaku just near the international date line.

The other three models have Sinlaku at about 170 E…moving it along a little bit slower. The EC model is the only one to keep Sinlaku south of 40 N.

Links: NOGAPS GFS ECMWF Met Office

What about the phase diagrams?

The GFS diagram already diagnoses an assymetric vortex. It  transitions Sinlaku to a cold core vortex just before the 21st, and then makes it symmetric again by 18Z on the 23rd.

The NOGAPS diagram also transitions to a cold core by the 21st, starting from an assymetric vortex. It maintains this fully extra-tropical storm throughout the forecast period.

The 12Z Met Office model diagram has Sinlaku just on the edge of being a cold core system. Towards the end of it’s forecast period, it also makes it more symmetric.

The plan is to continue to fly Sinlaku from 00Z (C-130) and 02Z (P-3) on the 20th. Hopefully this will capture and measure the continued transition.

Sinlaku is a Typhoon once again…and then back to a Tropical Storm

Friday, September 19th, 2008

As of 00Z on the 19th, Sinlaku was upgraded once again to a Typhoon by JTWC. Then, by 12Z on the 19th it was downgraded to a tropical storm

This Mimic animation shows Sinlaku’s eyewall development with convection building to it’s south, and then subsequent weakening:

MIMIC animation of Sinlaku from 12Z on the 18th to 12Z on the 19th. Notice how convection develops on its southwest side as it intensifies.

MIMIC animation of Sinlaku from 12Z on the 18th to 12Z on the 19th. Notice how convection develops on its southwest side as it intensifies.

Sinlaku is still under the duel effects of shear and strong upper-level outflow from the midlatitude westerlies. Both the divergence and shear plots are attached below:

IR MTSAT Image, upper-level AMVs and analyzed divergence. Valid 13Z on September 19th, 2008.
IR MTSAT Image, upper-level AMVs and analyzed divergence. Valid 13Z on September 19th, 2008
MTSAT IR Image and upper-level shear. Valid 13Z September 19th, 2008.

MTSAT IR Image and upper-level shear. Valid 13Z September 19th, 2008.

Again, Sinlaku’s motion is aligned fairly well along the shear axis, perhaps limiting it’s negative impact on its intensity somewhat. The enhanced outflow from the upper-levels and relatively high SSTs are competing with the shear. The shear will likely win out and Sinlaku will weaken.

Satcon shows the weakening as well, with the ADT producing much lower intensities than previous satcon analyses:

Satcon for Sinlaku. The ADT is currently producing weaker estimates than previous satcon estimates.

Satcon for Sinlaku. The ADT is currently producing weaker estimates than previous satcon estimates.

Yesterday and today the P-3 and C-130 will focus on Sinlaku and try and capture it’s ET. This is first time that extra-tropical transition has been captured by recon in the west pacific.

What about the forecast?

They will be the focus of subsequent blogs.

Sinlaku: 13Z, September 18th, 2008

Thursday, September 18th, 2008

Sinlaku is still churning away. It was briefly upgraded to a Typhoon at 00Z on the 18th, then downgraded back to a Tropical Cyclone.  According to JTWC, as of 12Z on the 18th, it was located near 31.0N 131.5E, moving 060 degrees at 09 kts. They analyze it at 55 kts with gusts to 70 kts.

Attached below is the standard IR/AMV/divergence plot valid 13Z on September 18th:

Although Sinlaku has continued outflow to the northeast, it’s flow is very well contained on the west side as it gets caught up in the midlatitude westerlies. The shear over Sinlaku, shown below, is very strong from the west:

The satcon analysis below shows Sinlaku’s recent intensity trend:

You can see the brief peak in intensity from JTWC (black curve) and the slight upward trend from SATCON and the ADT. Reading their prognostic reasoning, it appears JTWC re-intensified the storm based on recon data from TPARC.

Sinlaku may have re-intensified partially because its center has remained over water. This may allow it to maintain its tropical characteristics a bit longer than if it had passed over land.

As it begins ET, we will focus a bit on the tilt of its vortex. Currently, its low level center is a bit displaced to the southwest from the maximum convection as seen in the attached 85 GhZ and divergence plot:

The displacement isn’t huge, but the center (shown by the hurricane symbol, and the slightly circular pattern in the microwave image) is slightly over from the more intense microwave images and the divergence maximum. As ET happens, we’d expect more a vortex title. We’ll explore other ways to show this.

In the short term, the models are fairly consistent in bringing Sinlaku just south of the Japanese islands. There are some slight differences in terms of time and storm size, but the broad picture is fairly similar.

After Sinlaku leaves Japan, the models take a few different tacks with it’s track. The Met Office model and NOGAPS both bring Sinlaku up fairly far north and intensifying it, threathening the Aleutian Islands.

The ECMWF model merges Sinlaku with another midlatitude system, eventually moving toward Alaska.

The GFS takes a middle path: bringing Sinlaku up the Aleutians, but at a slower pace, and with less intensity than the Met Office.

It’s quite easy to see how uncertainties at this stage of forecasting can easily affect long-range forecasting downstream on the US coast.

And the phase diagrams? The GFS diagram begins to develop an assymetric core by the 19th, but does not really become cold core until the 24th of September!

The NOGAPS is faster: generating the assymetric core right away with Sinlaku becoming cold core just before the 20th.

The Met Office model diagram keeps it warm core throughout the shown forecast period.

How will Sinlaku interact with the midlatitute jets and outflow? When will it become extratropical? How strong will it get? These are questions that will need further investigation.

TCS043

Wednesday, September 17th, 2008

Attached is an IR animation for TCS043:

Taking a look at a two day animation (focus on TCS043 at about 15N 142E) you can see dirunal variation, as TCS043 strengthens around 12Z (22:00 Guam time) and weakens around 00Z (10 am Guam time). The short animation above is from 10Z - 15Z: near the convective maximum.

At this point, however, shear is the primary factor influencing TCS043:

The above plots show the shear (top) and divergence (bottom) over TCS043. The shear is consitently pushing the convection south. You can see this with the IR images, and with the location of maximum divergence. It’s unlikely to develop while under such strong shear.

The models are in two camps with this invest. The NOGAPS and GFS model have TCS043 developing and then recurving around (NOGAPS) and past (GFS) 140 E longitude. The 12Z ECWMF still has TCS043 moving west and interacting with the monsoon near the Philippians. Unlike the previous run, this run suggest hints of recurvature towards the end of the forecast period. The Met Office model, always the most reluctant developer, brings TCS043 westward and has a weaker interaction with that Phillipean convection.

The key to the recurve/no recurve difference seems to stem from a trough coming off of the China coast from the 20th-21st. The models with a deeper trough seem to be recurving the storm. The models without it seem to allow TCS043 to progress westward. We’ll have to keep an eye on this track difference in future runs.

Sinlaku strengthens and approaches Japan

Wednesday, September 17th, 2008

Sinlaku has intensified over the last few hours. The attached ADT estimate shows the change in MSLP and maximum sustained winds:

Advanced Dvorak Intensity Estimates for Tropical Storm Sinlaku.

Advanced Dvorak Intensity Estimates for Tropical Storm Sinlaku.

Here is the 13Z IR image, with upper-level AMVs and analyzed divergence:

You can see the Sinlaku’s sheared structure from the south-westerlies and westerly winds aloft. It still has healthy upper-level divergence and decent anticyclonic outflow aloft. The shear is very strong on this storm: nearly 35 to 45 knots above Sinlaku. The key may be storm motion: Sinlaku is moving to the northeast so  storm-relative shear is not as strong as the earth-relative shear. Also, the winds causing the shear, a midlatitude jet, are enhancing Sinlaku’s outflow.

The attached SSMIS 85 GHZ image (valid 10Z) and divergence plot show the enhanced convection and upper level divergence:

As of 12Z on the 17th, JTWC has Sinlaku at 28.9N 128.1E. It is moving 060 at 14kts with maximum sustained winds of 45 kts (gusts to 55 kts). They are forecasting it to intensity to 55 kts by 12Z on the 18th before weakening.

The models are fairly consistent about bringing Sinlaku into Japan as it is steered by the subtropical ridge to its east. The timing is fairly similar: they generally cross the southern islands before 12Z on the 18th, with many of the differences due to the size and structure of the analyzed storm. You can see the 00Z 850 hPa vorticity loops here for:

NOGAPS,GFS,Met Office, ECMWF.

The P-3 flew into Sinlaku yesterday..landing at 06Z on the 17th. Both the P-3 and the C-130 are planning to fly Sinlaku on 22Z on the 17th, landing at 06Z on the 18th to investigate ET. If Sinlaku stays over mainland Japan, they won’t be able to fly into the its center, but they’ll focus on the external environment.

The Falcon will fly at 03Z on the 18th and investigate Sinlaku’s outflow.

What is the predicted ET timing:

The current GFS phase space is shown here.  The GFS has Sinlaku developing an asymmetric core by just after the 19th, and becoming a full cold core system by the 21st.

The NOGAPS phase space shows slightly faster timing for the transition. The flights aren’t likely to capture SInlaku in full transition during these next few flights, but will perhaps capture it in the beginning of the process.

The EC model, in its 850 temperature loop shows some frontogenesis beginning at about 00Z on the 19th as Sinlaku reaches Japan, but not really developing until about the 20th and beyond.

Sinlaku: 12Z Sept 16, 2008

Tuesday, September 16th, 2008

According to JTWC, at 12Z, September, 16, 2008, Sinlaku is near 27.2N 124.6E with winds at 045 kt and gusts at 55 kts.

Attached is an IR image with AMVs and analyzed divergence:

Valid 14Z, September 16th, 2008.

Valid 14Z, September 16th, 2008.

Sinlaku is highly sheared at the moment. The wind diverges some aloft, and you can see a weak anticyclonic flow to Sinlaku’s northeast. The 0947 Quickscatt winds are still showing Sinlaku’s closed circulation at the surface.

Also, the latest SSMI pass (shown below) shows an intense convective center, but that center is displaced from the divergence maximum aloft.

85 GHZ SSMI image and upper-level analyzed divergence.

85 GHZ SSMI image and upper-level analyzed divergence.

This is another sign of a system affected by shear. Also, as Sinlaku has been nearly stationary for so long, it has upwelled lower SSTs to the surface, lessening its own fuel. Sinlaku is  currently centered under a region of relatively low shear (10-15 kts), but surrounded by strong shear to its north.

JTWC has it intensifying only slightly before it makes landfall near Japan. All of the primary models have Sinlaku striking Japan, but the details vary a bit by model.

The NOGAPS has it striking Japan just after 00Z on the 18th.

The GFS model has a much smaller storm. It brings Sinlaku farther south and east than the NOGAPS, and doesn’t hit Japan as directly mostly because it doesn’t make Sinlaku quite as large.

The ECMWF model is similar to the GFS although it seems to be a bit slower with Sinlaku’s progression to Japan.

The UK Met Office model seems to forecast Sinlaku at the same size as the NOGAPS (probably due to bogusing) but has timing similar to the GFS and the ECMWF model.

It’s interesting to see the NOGAPS being the fastest mover with Sinlaku, as that’s been contrary to the previous performance with these models.

And what about ET:

Bob Hart’s ET phase diagrams from the 06Z run of the GFS model is shown below:

Sinlakus phase diagram from the 06Z September 16th run of the GFS. Courtesy of Dr. Bob Hart (FSU) and Dr. Jenni Evans (PSU)

Sinlaku's phase diagram from the 06Z September 16th run of the GFS. Courtesy of Dr. Bob Hart (FSU) and Dr. Jenni Evans (PSU)

From this diagram and model analysis, Sinlaku still has a symmetric structure until about 12Z on the 18th. It does not really a develop cold core until the 20th. The Met Office model keeps it fairly warm-cored throughout the forecast time shown. The NOGAPS analysis is a little bit slower in bringing ET than the GFS.

The P-3 and C-130 are both scheduled to fly Sinlaku on the 17th. The P-3 will take off at 20Z on the 16th and return to Japan at 06Z on the 17th and fly box patterns, investigating the pre-warm front region of Sinlaku. The C-130 will fly the same schedule, but will only ferry to Japan for future investigations.

The DLR falcon will investigate Sinlaku’s outflow, flying from the 22Z on the 16th through 07Z on the 17th.

Perhaps they can capture some pre-extratropical conditions that will be valuable for understanding ET.