Major Typhoon SOUDELOR Heading for Taiwan

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WEDNESDAY: 05-AUG-15
(By Steve Gregory - Substituting for Dr. Masters and Bob Henson.)

MAJOR TYPHOON TO STRIKE TAIWAN FRIDAY

What was the strongest Super Typhoon of the year just 36 hours ago with top winds estimated near 200mph, has weakened to a Major, CAT 3 Storm some 460NM SSE of Okinawa as outflow, especially to the north, has weakened considerably and the upper level Outflow weakened proportionately. Even in the WPAC, Super Typhoons like SOUDELOR with extremely small ‘pinhole’ eyes (at one point, less than 4NM across) rarely are able to maintain their MAX intensity following a ERC (Eyewall Replacement Cycle) – and in this case, the significant reduction in the outflow Jet speeds has only accelerated the current weakening phase. In addition, the symmetric and well developed outflow pattern of SOUDELOR is likely being negatively impacted by developing INVEST 96W well to the east of SOUDELOR.

That said – as the storm continues on a generally westward heading (280˚-290˚), the global models show a significant increase in the poleward outflow speeds in 36-48 hrs which should lead to re-intensification – possibly to a CAT 4 intensity by the time it reaches Taiwan late Friday/early Saturday. With virtually every global and specialized Hurricane Forecast model in excellent agreement on the track, there is a very high probability of a direct, full-force strike to the Island nation. After crossing the Island, the cyclone should weaken to a CAT 2 before striking the mainland China coast.

Next UP: INVEST 96W

Another large, developing TC (INVEST 96W) is estimated near 18˚N/147˚E, still well east of the Mariana Islands, is likely to intensify into a Typhoon during the next 48 hrs as it’s already developing an outflow pattern aloft and is in an area of low shears and very warm SST’s.

TROPICAL STORM GUILLERMO CONTINUES TO WEAKEN

Former Hurricane GUILLERMO has continued to weaken over the past several days to Tropical Storm strength with sustained winds now estimated near 50Kts and is located about 280NM east of the Big Island. The storm is expected to pass parallel to, but north of, the Hawaiian Island chain on Thursday and Friday, and will likely have minimal impact on any of the Islands as all significant convection (and max winds) is now only found to the north of the cyclone center.

Numerous RECON flights - including G-IV missions – confirm the steady increase in westerly wind shear observed in Satellite (SAT) imagery over GUILLERMO. This has greatly disrupted the inner circulation field as the vortex now has a strong ‘tilt’ in the mid and upper levels, and a major degradation in high level outflow.

Considering the increasing shear environment and current trends, it would not be surprising to see the storm weaken to depression intensity by the time it passing north of Hilo, and could easily become a remnant Low well north of Honolulu by Friday.

THERE’S MORE COMING WHERE GUILLERMO CAME FROM…

The next system to potentially pose a threat to Hawaii is INVEST 92E, now near 12˚N/127W, or about 1,400NM SW of the southern tip of Baja. The system is still quite close to the ITCZ but should extradite itself from its influence within the next 24-36 hours, allowing the system to begin developing. The latest model runs call for the system to slowly intensify to Tropical Storm intensity in 36-48 hours, as it heads WNW. This system is at least 6-8 days away from it becoming a possible threat to Hawaii.

Several global models are calling for a series of cyclone formations in the EPAC over the next 10-14 days, all of which have the potential to threaten Hawaii. It certainly appears that this year’s strong El Niño environment will be producing numerous EPAC storms with a significant potential to reach the Islands.

TROPICAL ATLANTIC – BELIEVE IT OR NOT - IT REALLY IS HURRICANE SEASON

The Tropical Atlantic is ‘stirring’ – but don’t expect a cyclone formation anytime soon.

Even though former INVEST 94L can still be identified in the central Atlantic, and ‘silly’ INVEST 95L exits from any real concern – we do see a more active environment continuing to develop over the far eastern Atlantic, with a significant Tropical Wave (TW) now just off the African coast, with distinct mid-level rotation observed in the TPW imagery loops. However, this system is solidly embedded within the ITCZ, and considering its current track that will send it towards a more stable environment, it’s unlikely this system will be able to spin-up.

On the ‘plus’ side (for those anxious to have a bona-fide cyclone to track), conditions have become more conducive for cyclone formation over the past week or so. SST’s in the EATL have finally risen to a level that can support ongoing convection, and wind shear is generally low enough south of 20˚N to not be a major hindrance. Probably more importantly at this point is the very large drop-off in the SAL (Saharan Air Layer) flow that has been a major hostile force all summer as the warm, dry air layer has produced a very stable environment across much of the tropical Atlantic.

This seasonal drop-off in the SAL is likely to continue, though occasional surges are likely at times over the next few weeks, especially if/when especially strong TW’s come off the African coast at ‘higher’ latitudes – which typically happens by the end of AUG thru mid-September – coinciding with ‘Cape Verde Season’.

As I’ve pointed out in earlier posts, wind shear in the CARIB has been extremely high this season – primarily induced by the strong El Niño event in progress over the EPAC. This will likely to continue for the rest of Hurricane season, though no doubt, there will be some periods of reduced shear especially in SEP and early OCT.

For additional coverage on national weather, El Nino and other related topics - I will be posting a new Blog update late this afternoon on my own WU Blog.

**

Fig 1: 48 Hour Color Enhanced IR (infrared) image loop of Typhoon SOUDELOR


Fig 2: Water Vapor Imagery of SOUDELOR from earlier today highlighting the banding structure of the storm, along with cloud top Temps that are as low as -70˚C. The CDO signature has weakened compared to yesterday, and while not cloud filled, there are some low level clouds within the eye – characteristic of a weakening system.


Fig 3: WPAC SST’S (left) and total OHC (Ocean Heat Content - right) SST’s are well above levels needed to support a CAT 5 intensity, and remain above 30˚C until reaching the Taiwanese coast. OHC along the projected track for SOUDELOR does drop off some, but remains high enough to support a Major storm as long as the storm’s forward motion does not slow appreciably. A major slowdown (not expected) would lead to widespread, strong upwelling which could weaken the storm – or at least prevent any strengthening.


Fig 4: Micro-wave Image highlighting possible ERC. This early AM image shows the most intense convective feeder band and eye wall of SOUDELOR. On this image, you can see what appears to be major weakening of the inner eyewall as an outer wall develops.


Fig 5: Upper level Wind analysis from CIMSSshows a much reduced outflow jet towards the north, and a bit weaker equatorward jet which has led to the weakening observed over the past 36 hours. In addition, a developing outflow over INVEST 96W to the east of SOUDELOR is also interfering with the Typhoon’s outflow.


Fig 6: Navy Track and Intensity Forecast from this AM is in excellent agreement with all global and specialized hurricane model forecasts – especially on the track – with a direct hit to Taiwan expected by early Saturday. Note the forecast for an increase in intensity prior to landfall as upper level outflow – especially poleward – should increase in 36-48 hrs, allowing an increase in low level surface winds.


Fig 7: Last VIS image showing SOUDELOR on the far left, with developing INVEST 96W about 950NM east of SOUDELOR. It’s can be tough to determine which system’s circulation field will be most impacted by the other’s!


Fig 8: Color Enhanced IR image and Shear analysis of T.S. GUILLERMO shows most of the significant convection is now only found to the north of the storm, with wind shear values approaching 40Kts. With shears increasing to over 60Kts near Honolulu, GUILLERMO’s days are numbered.


Fig 9: Navy Track and Intensity Forecast for GUILLERMO calls for the tropical Storm to weaken to depression intensity in within 48-72 hrs. This is likely too generous – as the system is likely to weaken to Depression intensity within 36-48 hrs.

CLICK IMAGE to open full size image in a new window
Fig 10: Color Enhanced IR (infrared) image of the Tropical Atlantic The remnant disturbance that was INVEST 94L is still discernable as a very weak Low near the base of the TW along 48W which is westbound at about 15Kts. Aside from several other very weak TW’s, a stronger wave with mid-level rotation is located just off the African coast, but is solidly embedded within the ITCZ which is inhibiting development. Most notable in today’s overview of the tropical ATL is the major reduction in the SAL flow – with little dust filled air found anywhere over the ATL ocean. However, the forecast for the SAL (below) does show a strong, but limited SAL flow spreading over the EATL in the next day or two. While none of the global models call for this TW to develop into a cyclone, an upstream wave over central Africa and still a couple days away from reaching the coast, is forecast by the ECMWF to spin-up into a cyclone by early next week – though none of the other global models concurs with this outlook.



Fig 11: The TPW (Total Precipitable Water) Loop (Top) and latest image frame (bottom) highlights areas with deep layered moisture. ‘Bluish’ colors represent dryer air while the darker, ‘orange’ tones highlight areas of deep moisture in the column of air above the surface. The 72 hour looped imagery shows a clear rotation in vicinity of the African coast – embedded within the ITCZ.


Fig 12: Specialized ‘Dust’ focused imagery from the EUMETSAT product suite. The magenta/pinkish colors correspond to specific light wavelengths that have been shown to correlate with atmospheric dust.If you've been following my blogs this summer, you know by now there are quite a few different products that aim to highlight Dust and other aerosols associated with the SAL (Saharan Air Layer). Many of these products tend to ‘overdo’ dust concentration - for example, the Univ. Of Wisconsin CIMMSS product which tends to rely on moisture content analysis in the lower portion of the atmosphere. The above 24 hour loop tends to underplay actual dust content; but, the 3 different products I've posted this season, when used together, usually results in a fairly accurate analysis. While I haven’t posted any this season, even ‘normal’ Visible imagery taken early in the day, along with MODIS True Color imagery can do an excellent job of highlighting aerosol content. What makes the ABOVE imagery so useful is the simultaneous depiction of deep convection over Africa at hourly intervals, enabling us to get a good handle on Tropical Waves moving across the African continent. The strongly highlighted area of low-level dust north of the ITCZ is forecast to come off the African coast during the next day or two (See Below), while we can also see the strong area of convection over central Africa that the ECMWF is forecasting to develop into a cyclone early next week.


Fig 13: Specialized ‘Dust’ analysis / forecast from NASA calls for a strong burst of dust filled air over the next few days – but is significantly less ‘dense’ and ultimately less expansive than we’ve seen over the past couple months.

For additional coverage on national weather, El Nino and other related topics - I will be posting a new Blog update late this afternoon on my own WU Blog.

Steve