KoritheMan's WunderBlog

Tropical weather analysis - November 20, 2013

By: KoritheMan, 12:15 AM GMT on November 21, 2013

Melissa

Melissa finally made the transition to a tropical storm around 1200 UTC this morning. As of the latest NHC advisory, the following information was posted on the storm:

Wind: 50 mph, with higher gusts
Location: 37.2°N 44.9°W
Movement: ENE at 30 mph
Pressure: 988 mb

Now that Melissa is behaving like a tropical cyclone, it is exhibiting all of the features of one; upper-level outflow has finally developed in connection with the storm, primarily over the western semicircle, although there is some noticeable emanation taking place in the northern quadrant as well. Satellite estimates still support an intensity of around 45 kt. There was an ASCAT pass around 1330Z that showed seemingly reliable 40 kt wind vectors not far southeast of the center; given the low bias of that instrument, and no appreciable change in organization since then, it's probably safe to assume that Melissa is still hovering around 45 kt, particularly with the acceleration of the forward motion in mind. Convection has diminished somewhat near the center, with more prominent bands in the north replacing the central convection.



Figure 1. Latest infrared satellite image of Tropical Storm Melissa. Image credit: NOAA's Satellite Services Division (SSD).

Although convection is weakening, waters are cooling, and shear is increasing, Melissa is a rather fast-moving tropical cyclone, and such systems normally weaken only slowly, even over non-tropical environments. My forecast will thus carry tropical storm force winds in connection with Melissa and its post-tropical remnants for the next 48 hours. As then extratropical Melissa dives southeastward toward Portugal and Spain, winds are expected to drop below tropical storm force, in part because a deceleration in the forward motion is anticipated during that time. My intensity forecast is fairly good agreement with the 12z GFDL, particularly near the end of the forecast. Non-tropical restrengthening is not expected since Melissa is forecast to become wedged between two ridges near western Europe, and remain quite far from any baroclinic forcing associated with an upper-level trough moving over the western and central Atlantic. After 72 hours, the extratropical remnants of Melissa are expected to dissipate just off the coast of western Portugal or northern Spain, bringing only residual shower activity and perhaps locally gusty winds to those countries.

Melissa is essentially moving in tandem with the latest National Hurricane Center forecast track, and the synoptic steering pattern still appears to be quite straightforward. There aren't much notable differences in the global model guidance pertaining to Melissa's ultimate trajectory, with the models in agreement that the extratropical remnants of formerly tropical Melissa will accelerate east-northeastward over the next couple of days, before slowing and moving southeastward toward Portugal and Spain. The models are in so good agreement, in fact, that there are nary any significant speed differences, which is normally not the case with high-latitude systems accelerating in the westerlies. The GFS has come into even better agreement with the ECMWF today, and my forecast follows those models closely, and is also similar to the latest TVCE model consensus.

Intensity forecast and positions

INITIAL 11/20 0000Z 37.5°N 44.2°W 45 KT 50 MPH
12 hour 11/21 1200Z 39.8°N 40.4°W 45 KT 50 MPH
24 hour 11/22 0000Z 41.5°N 35.0°W 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
36 hour 11/22 1200Z 43.6°N 28.2°W 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
48 hour 11/23 0000Z 42.9°N 20.5°W 35 KT 40 MPH...POST-TROPICAL/EXTRATROPICAL
72 hour 11/24 0000Z 40.6°N 14.1°W 30 KT 35 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 11/25 0000Z...ABSORBED

Track forecast



Figure 2. My forecast track for Melissa.

2013 Atlantic hurricane season Tropical Storm Melissa

Updated: 12:18 AM GMT on November 21, 2013

Permalink

Tropical weather analysis - November 19, 2013

By: KoritheMan, 2:37 AM GMT on November 20, 2013

Melissa

Melissa continues as a subtropical storm over the central Atlantic, and is no threat to land areas. As of the latest NHC advisory, the following information was available on the storm:

Wind: 65 mph, with higher gusts
Location: 33.0°N 53.7°W
Movement: NE at 16 mph
Pressure: 982 mb

The satellite presentation of Melissa has degraded rather significantly this evening. Convective cloud tops have warmed considerably, with only a very fragmented band of tops colder than -40C a short distance north of the center. While convection has been shallow, what convection has existed has been ongoing fairly close to the center in bands. This would ordinarily argue for tropical characteristics, but water vapor imagery suggests that Melissa is still deeply involved with a weakening upper cold low. Satellite estimates have not changed much, with TAFB still giving a classification of 3.0/45 kt. I should note that the 0z ATCF file from the NHC shows Melissa as a 50 kt storm, rather than a 55 kt storm, so I used that for the initial intensity below.



Figure 1. Latest infrared satellite image of Subtropical Storm Melissa. Image credit: NOAA's Satellite Services Division (SSD).

Time is just about out for Melissa to become a tropical cyclone. AMSU temperature profiles indicate that the cyclone has a rather deep warm core at about 500 mb, but the upper troposphere has been slow to warm above that level over the last few days, likely because Melissa remains involved with the upper low, which has in itself helped to inject dry air and subsident flow into the system. The dry air, in turn, has not allowed for Melissa to generate persistently cold thunderstorms to sufficiently warm the upper troposphere and make the transition to a tropical cyclone; there are still no signs of anticyclonic outflow, which is another indicator that Melissa remains subtropical. While the SHIPS model's analysis of 24C underlying sea surface temperatures are likely falsely inflated toward the cold side, Melissa has already crossed the 26C isotherm. From this point onward, waters cool significantly, which should put an end to additional intensification, and with any luck, the epic fail that is the 2013 Atlantic hurricane season. The global model guidance continues to indicate that the environment over the north Atlantic will not be adequately baroclinic to promote some non-tropical restrengthening later in the period; instead, Melissa is likely to weaken over cold water and strong shear as it remains quite distant from an upper-level trough moving over the western Atlantic. Most of the guidance suggests that the cyclone will become absorbed into the deepening trough by the 96 hour mark, and it is possible that the merger could be complete in as little as 72 hours. It is possible that Melissa could become a non-convective remnant low at any time over the next 24 hours, prior to the point of extratropical transition.

Melissa's center appears to be somewhat broad based on microwave and satellite data, but lacking convection it is still reasonably easy to follow. Melissa appears to still be moving northeastward ahead of the aforementioned trough, but a comparison of the current motion to the track contained in the previous NHC advisory package suggests that Melissa could be moving ever so slightly to the right of the track, so my forecast was shifted a little eastward to reflect this. The models have come into better agreement on where Melissa is going to move in the latter portion of the forecast period, with the GFS no longer a western outlier. With the ECMWF and GFS now in tow, confidence in the forecast track at longer ranges has increased. It should be noted that the GFS is still well to the left of the ECMWF at longer ranges, but has come into the fold enough to consider it more or less in synch. My forecast track tonight is significantly east of the one I made yesterday.

Intensity forecast and positions

INITIAL 11/20 0300Z 33.5°N 52.7°W 50 KT 60 MPH
12 hour 11/20 1200Z 35.7°N 48.5°W 50 KT 60 MPH
24 hour 11/21 0000Z 38.0°N 44.7°W 45 KT 50 MPH
36 hour 11/21 1200Z 40.9°N 38.0°W 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
48 hour 11/22 0000Z 43.5°N 30.5°W 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
72 hour 11/23 0000Z 49.4°N 25.6°W 35 KT 40 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 11/24 0000Z...ABSORBED

Track forecast



Figure 2. My forecast track for Melissa.

Subtropical Storm Melissa 2013 Atlantic hurricane season

Permalink

Tropical weather analysis - November 18, 2013

By: KoritheMan, 3:51 AM GMT on November 19, 2013

Melissa

Subtropical Storm Melissa formed over the central Atlantic today from a non-tropical area of low pressure. As of the latest NHC advisory, the following information was available on Melissa:

Wind: 60 mph, with higher gusts
Location: 30.3°N 54.7°W
Movement: NW at 8 mph
Pressure: 985 mb

The cloud pattern connected to Melissa is still decidedly non-tropical. While the outer convective bands about 100 miles south of the center seen earlier this evening have largely dissipated and convection has formed closer to the center, the cloud tops encompassing this new convection are not particularly cold given the high latitude of Melissa. TAFB furnished a satellite classification of 3.0 as of 0z. While this would normally portend surface winds of only 45 kt, the Dvorak technique only works for systems that are fully tropical, which Melissa is not. A recent AMSU microwave pass shows me that Melissa still lacks an inner core.



Figure 1. Latest infrared satellite image of Subtropical Storm Melissa. Image credit: NOAA's Satellite Services Division (SSD).

While scatterometer fixes have been somewhat patchy, the data I've been able to collect suggests that the radius of maximum winds has contracted compared to 24 hours ago, but Melissa is still embedded within a broader-scale cyclonic low over the central Atlantic, as denoted by surface and satellite observations. AMSU vertical temperature profiles indicate that Melissa is putting up a valiant fight in making the transition to a tropical storm, warming in the upper troposphere has been slow and perhaps unsteady. In addition, water vapor imagery and UW-CIMSS 200 mb vorticity data suggest that Melissa is still well-involved with a large upper-level low pressure system. The SHIPS model analyzed areal sea surface temperatures of only about 25.5C, which appears to be about 1.5C too cold given sea surface temperature maps. Hence, I have high hopes that Melissa will make the transition to a tropical storm on Tuesday, and while, not explicitly shown yet, there is a chance that the cyclone could briefly reach hurricane strength, perhaps up to about 70 kt; this would occur as Melissa moves underneath the axis of a narrow upper ridge forecast to develop over the system in about 24 hours. Subsequently, as the cyclone enters higher latitudes, moves over cold water, and experiences increases in vertical shear, weakening is anticipated. The current model guidance does not show an environment that really screams out "baroclinic forcing" to me, so a steady decline in intensity is expected even after the system becomes extratropical. There is the possibility that Melissa could become a non-convective remnant low at the 48 hour mark before it interacts with an upper-level trough moving off the eastern United States, but the timing and magnitude of this transition is difficult to predict.

Melissa still appears to be moving northwestward, but a turn to the north is expected to manifest very soon as a deep-layer trough moves off the east coast of the United States within the next 12-24 hours. Melissa is expected to move northward only briefly, as the trough will impart mid-level southwesterly flow to the cyclone and accelerate it northeast to east-northeast. The model guidance has no real conundrums except for the end of the period, when the GFS and ECMWF differ significantly on whether Melissa will continue eastward toward western Europe, or whether it will continue north into Greenland. My forecast track compromises the possibilities, lacking any reason to favor one scenario over the other, and is a little left of the current NHC prediction.

Due to the limitations of the track map on which I draw my forecast tracks, I am unable to furnish a forecast point out to day five.

Intensity forecast and positions

INITIAL 11/19 0300Z 30.3°N 54.7°W 50 KT 60 MPH
12 hour 11/19 1200Z 31.5°N 53.8°W 55 KT 65 MPH...TROPICAL
24 hour 11/20 0000Z 34.4°N 51.2°W 60 KT 70 MPH
36 hour 11/20 1200Z 37.1°N 48.2°W 60 KT 70 MPH
48 hour 11/21 0000Z 40.5°N 44.5°W 55 KT 65 MPH
72 hour 11/22 0000Z 45.1°N 40.0°W 50 KT 60 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 11/23 0000Z 50.7°N 41.0°W 45 KT 50 MPH...POST-TROPICAL/EXTRATROPICAL
120hour 11/24 0000Z 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL

Track forecast



Figure 2. My forecast track for Melissa.

2013 Atlantic hurricane season Subtropical Storm Melissa

Permalink

Tropical weather analysis - November 6, 2013

By: KoritheMan, 2:21 AM GMT on November 07, 2013

Haiyan

Dangerous Super Typhoon Haiyan is heading steadily toward the central Philippines. As of the latest JTWC advisory, the following information was available on the typhoon:

Wind: 175 mph, with higher gusts
Location: 8.6°N 132.8°E
Movement: WNW at 18 mph
Pressure: 911 mb
Category: 5 (Saffir-Simpson Hurricane Wind Scale)

The satellite presentation is, in a word, spectacular. After a brief hiccup in the southern eyewall from about 2000 to about 2315 UTC, convection has redeveloped around the southern eye, and Haiyan appears to be on course to maintain its intensity. Upper-level outflow is exceptionally well-defined everywhere except the east, where it is somewhat restricted, but expanding. In addition, a large convective band extends to the west of the center; given the small size of the cyclone, it is presumed that there are no tropical storm force sustained winds occurring within this band, although scatterometer data suggests that the winds could be sustained at 25 to 35 mph in that band.



Figure 1. Latest infrared satellite image of Super Typhoon Haiyan. Image credit: NOAA's Satellite Services Division (SSD).

There do not appear to be any obvious factors to immediately weaken Haiyan. Oceanic heat content in this portion of the western Pacific is extremely significant; in addition, the near-storm vertical shear appears to be low as evidenced by the well-organized cloud and outflow patterns, and there does not appear to be any dry air that could get entrained into the circulation. The one fly in the ointment that is, unfortunately, extremely difficult to predict but common of intense typhoons like Haiyan, is a possible eyewall replacement cycles, or even multiple ones. I have literally no skill to anticipate these changes, and neither do any of the global and dynamical models. Primarily because of this ignorance, my forecast will keep Haiyan at 150 kt during the next 12 hours, followed by slow weakening after that as Haiyan interacts with land and possibly undergoes a concentric eyewall cycle (based primarily on timing, as cyclones this intense cannot normally maintain such obscene intensities for very long). However, I want to emphasize that I expect Haiyan to be at or near Category 5 intensity (Saffir-Simpson Hurricane Wind Scale) at landfall. Of course, there is enough uncertainty in the inner core evolution of such an intense typhoon that the winds could theoretically be 20 to 30 mph lower at landfall. Once the cyclone emerges over the South China Sea, a steady weakening trend is expected as dry air and subsident flow increases and oceanic heat content drops off sharply west of 115°E. There does not appear to be a lot of vertical shear over the South China Sea in the GFS model fields during those time ranges, but shear forecasts are riddled with immense uncertainty even a day out, and I would not be surprised if southwesterly shear increased even modestly ahead of the next upper-level trough. It should be noted that my forecast track and the JTWC track takes Haiyan inland over Vietnam to a position where the cyclone center lies in close proximity to the adjacent South China Sea, which could help to promote sustained tropical storm force winds along the coast all the way up to day five in the forecast period, and that is reflected below.

Haiyan appears to be moving quickly west-northwest, and is more or less on track. The strong subtropical ridge to the north extends all the way into the upper troposphere, and Haiyan will follow its southern periphery over the next several days, making landfall in the central Philippines by Thursday evening (United States local time). After that time, the typhoon is forecast to continue heading in that general direction while steadily gaining additional latitude. Beyond about 48 hours, an upper-level trough over China is expected to weaken the ridge a little and cause Haiyan to slow its forward speed. Landfall is likely to occur at or just after 72 hours in northern Vietnam. My forecast track is in good agreement with the 18z GFS, and is fairly similar to the latest JTWC track.

Haiyan passed not too far to the north of the island of Palau around 15 or 16 UTC, and the southern eyewall raked the island. While damage is by no means going to be catastrophic on the island (we're talking about a westward-moving typhoon, which would tend to idealize the strongest winds to the northern eyewall) and especially compared to what it will be farther west, damage was undoubtedly significant on the northern reaches of the island, where sustained winds probably reached 80 to 100 mph. We will need to wait a few days before the extent of the damage on the island can be determined.

Haiyan is a fairly small tropical cyclone, with 34 kt winds extending outward only up to perhaps no more than about 130 miles in the northeastern semicircle. Since the cyclone will be slow to gain latitude, and will only barely be above 10°N at landfall in the Philippines, I do not imagine we will see a Katrina or Ike-size storm hitting the Philippines. If true, this means that the core of strongest winds will be confined to a fairly small area along the northern and northeastern eyewall. However, if a concentric eyewall cycle occurs prior to or just after landfall, the outer wind radii will increase, spreading out damaging winds over a larger area. Rainfall and flooding should be fairly limited over the Philippines due to the fast forward motion of Haiyan; however, the rains could be heavier and cause extensive flooding over Vietnam, when the cyclone is likely to encounter an upper-level trough and decelerate.

Intensity forecast and positions

INITIAL 11/07 0000Z 8.7°N 133.8°E 150 KT 175 MPH
12 hour 11/07 1200Z 9.5°N 128.3°E 150 KT 175 MPH
24 hour 11/08 0000Z 10.9°N 124.1°E 135 KT 155 MPH...INLAND
36 hour 11/08 1200Z 11.9°N 120.1°E 120 KT 140 MPH...OVER WATER
48 hour 11/09 0000Z 14.9°N 114.2°E 105 KT 120 MPH
72 hour 11/10 0000Z 90 KT 105 MPH
96 hour 11/11 0000Z 65 KT 75 MPH...INLAND
120hour 11/12 0000Z 35 KT 40 MPH...INLAND

Track forecast



Figure 2. My forecast track for Haiyan. Note that I couldn't find a track map other than the one I found above, so because of the limitations of that map, I am unable to assess latitudinal and longitudinal points subsequent to the 48 hour mark, but my forecast track is pretty similar to the JTWC at later periods.

2013 Pacific typhoon season Super Typhoon Haiyan

Permalink

Tropical weather analysis - November 3, 2013

By: KoritheMan, 4:10 AM GMT on November 04, 2013

Sonia

Tropical Storm Sonia continues to race toward the coast of mainland Mexico. As of the latest NHC advisory, the following information was available on the tropical storm:

Wind: 40 mph, with higher gusts
Location: 23.2°N 108.1°W
Movement: NNE at 17 mph
Pressure: 1004 mb

At first glance Sonia may appear to be well-organized, but it's actually not. Satellite, microwave, and radar data from Guasave on the southwestern mainland near the projected landfall point show a circulation that is elongated and exposed to the southwest of the deep convection, with the center actually remaining outside the -70 to -80C cloud tops persisting in the northern semicircle. 0z satellite estimates continue to support tropical storm strength, and it is not yet likely that Sonia has weakened to a tropical depression.



Figure 1. Latest infrared satellite image of Tropical Storm Sonia. Image credit: NOAA's Satellite Services Division (SSD).

UW-CIMSS diagnoses about 40 to 45 kt of shear over Sonia, but since that area of the world does not see routine upper air data like we do here in the United States, I find it likely that this figure is exaggerated; the cloud pattern is not quite convincing enough for me to bite on that just yet. Regardless, both the SHIPS and the GFS show the shear increasing even further, with the former even suggesting the shear could get as high as 73 kt in 36 hours. Even if the shear does not become its own hurricane and follow that prediction, it's still likely to rise to at least 40 to 50 kt very soon. These very harsh environmental conditions will not only help to interject dry air into the system from the southwest, they will also assist the Mexican plateau in choking the life out of Sonia. Virtually all of the global models show Sonia's 850 mb circulation dissipating even before the 24 hour mark, and I see no reason to provide a forecast point beyond that for the sake of continuity.

Sonia appears to be moving north-northeast, pretty much on track with the latest NHC prediction. The models have come a little to the right compared to yesterday, and my forecast will follow suit, ending up nearly on top of the official National Hurricane Center prediction.

Since Sonia is becoming a heavily sheared, poorly-organized tropical cyclone (not that it was ever not that to begin with), the strongest winds and heaviest rains will be felt well to the north and northeast of the center in the area of strong convection. Lacking a circulation to help maintain enough momentum to transport strong winds to the surface from aloft, the actual deep convection will probably fail to produce tropical storm force winds along the coast in the tropical storm warning area, but interests there should exercise caution just in case that scenario does not verify.

The primary hazard from Sonia is the potential for torrential rains capable of causing flash flooding and mudslides in areas of mountainous terrain. Sonia may enhance moisture over the southwestern United States and southern plains over the next few days as it interacts with a frontal boundary approaching from the west.

Intensity forecast and positions

INITIAL 11/04 0300Z 23.2°N 108.1°W 35 KT 40 MPH
12 hour 11/04 1200Z 25.5°N 107.4°W 25 KT 30 MPH...INLAND
24 hour 11/05 0000Z...DISSIPATED

Track forecast



Figure 2. My forecast track for Sonia.



NHC storm information

000
WTPZ33 KNHC 040231
TCPEP3

BULLETIN
TROPICAL STORM SONIA ADVISORY NUMBER 12
NWS NATIONAL HURRICANE CENTER MIAMI FL EP182013
700 PM PST SUN NOV 03 2013

...SONIA WEAKENS A LITTLE AS IT APPROACHES MAINLAND MEXICO...


SUMMARY OF 700 PM PST...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...23.2N 108.1W
ABOUT 115 MI...185 KM E OF THE SOUTHERN TIP OF BAJA CALIFORNIA
ABOUT 115 MI...190 KM SSW OF CULIACAN MEXICO
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...NNE OR 30 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* MAZATLAN TO ALTATA

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* NORTH OF ALTATA TO TOPOLOBAMPO

INTERESTS IN BAJA CALIFORNIA SUR AND ELSEWHERE IN WEST-CENTRAL
MAINLAND MEXICO SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 700 PM PST...0300 UTC...THE CENTER OF TROPICAL STORM SONIA WAS
LOCATED NEAR LATITUDE 23.2 NORTH...LONGITUDE 108.1 WEST. SONIA IS
MOVING TOWARD THE NORTH-NORTHEAST NEAR 17 MPH...28 KM/H...AND THIS
MOTION IS EXPECTED TO CONTINUE ON MONDAY. ON THE FORECAST
TRACK...THE CENTER OF SONIA SHOULD REACH THE COAST OF MAINLAND
MEXICO WITHIN THE WARNING AREA BY EARLY MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/H...WITH HIGHER
GUSTS. SOME ADDITIONAL SLIGHT WEAKENING IS POSSIBLE BEFORE SONIA
REACHES THE COAST OF MAINLAND MEXICO...AND RAPID WEAKENING IS
EXPECTED AFTER LANDFALL. SONIA IS FORECAST TO DISSIPATE OVER
MEXICO ON MONDAY AFTERNOON.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 35 MILES...55 KM
FROM THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1004 MB...29.65 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED IN THE WARNING AREA
TONIGHT AND EARLY MONDAY. TROPICAL STORM CONDITIONS ARE POSSIBLE IN
THE WATCH AREA TONIGHT AND EARLY MONDAY.

RAINFALL...SONIA IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS OF
3 TO 6 INCHES...WITH ISOLATED MAXIMUM AMOUNTS OF 10 INCHES...IN
PORTIONS OF THE MEXICAN STATES OF SINALOA...WESTERN DURANGO...AND
SOUTHERN CHIHUAHUA. THESE RAINS MAY PRODUCE LIFE-THREATENING FLASH
FLOODS AND MUD SLIDES.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...1000 PM PST.
NEXT COMPLETE ADVISORY...100 AM PST.

$$
FORECASTER PASCH

2013 Pacific hurricane season Tropical Storm Sonia

Updated: 4:26 AM GMT on November 04, 2013

Permalink

Tropical weather analysis - November 3, 2013

By: KoritheMan, 5:13 AM GMT on November 03, 2013

Tropical Depression Eighteen-E

Tropical Depression Eighteen-E remains weak just south of Baja California Sur. As of the 0300Z NHC advisory, the following information was provided on the system:

Wind: 35 mph, with higher gusts
Location: 18.3°N 110.1°W
Movement: NW at 6 mph
Pressure: 1006 mb

The depression continues to struggle, to say the least. While the shear appears to have decreased a little over the last 24 hours as evidenced by expanding cirrus outflow to the east, it has not diminished completely yet so that it's still acting to retard development. In addition, water vapor imagery and UW-CIMSS TPW data indicate that the cyclone has begun to ingest a somewhat drier airmass to the east than was apparent this time yesterday. The highest satellite classification at 0z was from TAFB, which came in at 2.5. While this would normally portend tropical storm strength, I much prefer the more conservative SAB estimate, which keeps the system as a tropical depression. An ASCAT pass just before 17z indicated that the circulation is quite elongated, particularly to the west.



Figure 1. Latest infrared satellite image of Tropical Depression Eighteen-E. Image credit: NOAA's Satellite Services Division (SSD).

Water vapor imagery suggests that the upper-tropospheric flow downstream from the depression is likely about to change from easterly to southwesterly. Coincident with the system's seemingly imminent northward turn, this change in the upper-level winds could briefly allow a narrow window of strengthening, perhaps to a minimal tropical storm if we're lucky. An alternative scenario, and probably more likely one, is that the depression fails to intensify further due to its sprawling nature and pulsating convection. While the National Hurricane Center official forecast shows the depression weakening before landfall, I'm somewhat skeptical that the sharp increase in 200 mb southwesterlies shown by the GFS and SHIPS will increase in time for that, with the distinct possibility existing that the cyclone may already be inland when the stronger shear arrives.

The center of the depression is difficult to locate yet again, even with reliable microwave images, but extrapolation and a hint of cyclonic turning in the area suggests that the low-level center is probably in the general vicinity of where the National Hurricane Center placed it. Regardless of the specifics of the rather broad circulation, the depression should turn northward very soon, as water vapor imagery and UW-CIMSS steering data indicate that the mid-level ridge over northern Mexico has progressed eastward enough to the point that it should no longer be considered a significant factor in the track. A northeastward turn is expected to commence shortly after the birth of the northward turn, with virtually all of the global and dynamical models bringing the system to the coast by Monday morning. My forecast track is quite similar to the National Hurricane Center prediction, and is close to the latest ECMWF model prediction.

It should be noted that, although tropical storm watches exist for a portion of southwestern mainland Mexico, it is entirely possible that these winds will not reach the coast. Moreover, although I don't expect the strongest shear to arrive until just after the system moves inland, that doesn't mean I anticipate the 200 mb winds to be favorable at the 36 hour mark; this means that the cyclone will likely be elongated southwest to northeast in its precipitation field, with the strongest winds and heaviest rains occurring not along the immediate coast, but over areas of mountainous terrain that lie just inland from the coast.

The remnants of the depression may enhance rainfall potential over the southwestern United States around midweek as the mid-level remnants interact with an approaching frontal boundary.

Intensity forecast and positions

INITIAL 11/03 0300Z 18.3°N 110.1°W 30 KT 35 MPH
12 hour 11/03 1200Z 19.4°N 110.2°W 30 KT 35 MPH
24 hour 11/04 0000Z 21.2°N 109.3°W 35 KT 40 MPH
36 hour 11/04 1200Z 24.3°N 107.8°W 35 KT 40 MPH...APPROACHING THE COAST
48 hour 11/05 0000Z 27.6°N 106.4°W 15 KT 15 MPH...INLAND POST-TROPICAL/REMNANT LOW
72 hour 11/06 0000Z...DISSIPATED

Track forecast



Figure 2. My forecst track for Tropical Depression Eighteen-E.

NHC storm information

000
WTPZ33 KNHC 030233
TCPEP3

BULLETIN
TROPICAL DEPRESSION EIGHTEEN-E ADVISORY NUMBER 8
NWS NATIONAL HURRICANE CENTER MIAMI FL EP182013
800 PM PDT SAT NOV 02 2013

...DEPRESSION MOVING NORTHWESTWARD...


SUMMARY OF 800 PM PDT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...18.3N 110.1W
ABOUT 320 MI...510 KM S OF THE SOUTHERN TIP OF BAJA CALIFORNIA
ABOUT 480 MI...770 KM SSW OF CULIACAN MEXICO
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...NW OR 320 DEGREES AT 6 MPH...9 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* TOPOLOBAMPO TO LA CRUZ

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

INTERESTS IN BAJA CALIFORNIA SUR AND ELSEWHERE IN WEST-CENTRAL
MAINLAND MEXICO SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 800 PM PDT...0300 UTC...THE CENTER OF TROPICAL DEPRESSION
EIGHTEEN-E WAS LOCATED NEAR LATITUDE 18.3 NORTH...LONGITUDE 110.1
WEST. THE DEPRESSION IS MOVING TOWARD THE NORTHWEST NEAR 6 MPH...9
KM/H. A TURN TOWARD THE NORTH AND NORTH-NORTHEAST AND AN INCREASE
IN FORWARD SPEED ARE EXPECTED BY LATE SUNDAY. ON THE FORECAST
TRACK...THE CENTER OF THE CYCLONE WILL PASS SOUTH OF THE SOUTHERN
TIP OF THE BAJA CALIFORNIA PENINSULA LATE SUNDAY...AND APPROACH THE
COAST OF MAINLAND MEXICO WITHIN THE WATCH AREA EARLY MONDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 35 MPH...55 KM/H...WITH HIGHER
GUSTS. THE DEPRESSION COULD BECOME A TROPICAL STORM TONIGHT OR
SUNDAY.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB...29.71 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE IN THE WATCH AREA
BY EARLY MONDAY.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...1100 PM PDT.
NEXT COMPLETE ADVISORY...200 AM PDT.

$$
FORECASTER BRENNAN

2013 Pacific hurricane season Tropical Depression Eighteen-E

Permalink

Tropical weather analysis - November 2, 2013

By: KoritheMan, 6:12 AM GMT on November 02, 2013

Tropical Depression Eighteen-E

Tropical Depression Eighteen-E has not changed much as of the 0300Z NHC advisory:

Wind: 35 mph, with higher gusts
Location: 16.9°N 108.4°W
Movement: NNW at 3 mph
Pressure: 1006 mb

The depression is not well-organized, with satellite and microwave data depicting multiple embedded swirls encompassing the broader cyclonic gyre comprising the system. Satellite estimates do not support tropical storm strength, and earlier scatterometer data during the evening suggested that the strongest winds were located to the west of the center, undoubtedly due to 15-20 kt of easterly shear as diagnosed by UW-CIMSS. There are two clusters of convection currently ongoing west and north of the center, but I am not apt to call either of these features curved bands. Given the persistence of the northern cluster, I would look for a possible center reformation in that area, where the shear appears to be less.



Figure 1. Latest infrared satellite image of Tropical Depression Eighteen-E. Image credit: NOAA's Satellite Services Division (SSD).

The depression presents me with a tricky intensity forecast this evening. The easterly shear over the system will likely inhibit development in the near-term, but the 0z GFS shows a more favorable 200 mb wind pattern evolving during the next 24 hours, potentially allowing strengthening while over warm sea surface temperatures. However, it is notable that the upper air pattern in the 18z GFS looks much more unfavorable than the one at 0z, with the shear not forecast to decrease until about a day or less before landfall. I am not ready to jump on the 0z GFS as completely credible just yet, given the current hostile environment and lack of organization of the depression, so I will base my forecast more on the 18z GFS for now. If the shear decreases faster than forecast, the cyclone could reasonably get to 45 or 50 kt before making landfall. One other potential complicating factor for intensification is an area of dry air to the west of the depression. While this could delay development somewhat, the upper-level flow across the cyclone is easterly from a moister airmass to the east, a situation that is not conducive for significant dry air entrainment. After landfall, the depression is forecast to quickly dissipate over the rugged terrain of southwestern Mexico, although a remnant mid-level circulation capable of dropping heavy rains and causing flooding will likely linger for another couple of days. Another complicating factor is the large size of the depression, which may inhibit swifter intensification even if the shear abates as the 0z GFS forecasts.

The center has not exactly been easy to locate; fortunately, a couple of well-timed microwave passes gave an indication of where the center might be based on where the NHC officially has it. But again, I note that there are numerous embedded swirls within the cyclonic circulation comprising the depression, making any estimate of the center (my own is given below) highly uncertain; even the microwave passes were inconclusive. Assuming the depression does not reform to the north, it should continue a gradual recurve around the western periphery of the subtropical ridge which is forecast to shift eastward over the next 24 hours as a very large upper-level cyclone a few hundred miles off the coast of California moves northeastward and fragments into a trough. Landfall should occur over mainland southwestern Mexico in the Puerto Vallarta area in about two and a half days, possibly sooner. If the depression reforms to the north, the immediate track may bend a little bit to the left before the westerlies grab it; this would increase the threat to southern Baja, which currently lies west of the official NHC forecast track. My own track is a little to the east of the current NHC prediction, as I feel the upper cyclone will exert more of a poleward influence than currently expected.

Tropical storm watches and warnings will probably be issued by the government of Mexico for southern Baja California Sur and mainland southwestern Mexico later today, since the average lead time for a tropical storm warning in the eastern Pacific is 36 hours, while the average lead time for a tropical storm watch is 48 hours.

Intensity and forecast positions

INITIAL 11/02 17.0°N 109.0°W 0600Z 30 KT 35 MPH
12 hour 11/02 17.7°N 109.7°W 1800Z 30 KT 35 MPH
24 hour 11/03 18.4°N 110.3°W 0600Z 35 KT 40 MPH
36 hour 11/03 19.5°N 110.3°W 1800Z 35 KT 40 MPH
48 hour 11/04 22.9°N 108.3°W 0600Z 40 KT 45 MPH
72 hour 11/05 28.5°N 105.4°W 0600Z 25 KT 30 MPH...INLAND POST-TROPICAL/REMNANT LOW
96 hour 11/06 0600Z...DISSIPATED

Track forecast



Figure 2. My forecast track for Tropical Depression Eighteen-E.

2013 Pacific hurricane season Tropical Depression Eighteen-E

Permalink

About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.

Local Weather

Light Drizzle
78 °F
Light Drizzle